On the morning of August 7, 2014, a team of fighters from the Islamic State, riding in pickup trucks and purloined American Humvees, swept out of the Iraqi village of Wana and headed for the Mosul Dam. Two months earlier, isis had captured Mosul, a city of nearly two million people, as part of a ruthless campaign to build a new caliphate in the Middle East. For an occupying force, the dam, twenty-five miles north of Mosul, was an appealing target: it regulates the flow of water to the city, and to millions of Iraqis who live along the Tigris. As the isis invaders approached, they could make out the dam’s four towers, standing over a wide, squat structure that looks like a brutalist mausoleum. Getting closer, they saw a retaining wall that spans the Tigris, rising three hundred and seventy feet from the riverbed and extending nearly two miles from embankment to embankment. Behind it, a reservoir eight miles long holds eleven billion cubic metres of water.

A group of Kurdish soldiers was stationed at the dam, and the isis fighters bombarded them from a distance and then moved in. When the battle was over, the area was nearly empty; most of the Iraqis who worked at the dam, a crew of nearly fifteen hundred, had fled. The fighters began to loot and destroy equipment. An isis propaganda video posted online shows a fighter carrying a flag across, and a man’s voice says, “The banner of unification flutters above the dam.”

The next day, Vice-President Joe Biden telephoned Masoud Barzani, the President of the Kurdish region, and urged him to retake the dam as quickly as possible. American officials feared that isis might try to blow it up, engulfing Mosul and a string of cities all the way to Baghdad in a colossal wave. Ten days later, after an intense struggle, Kurdish forces pushed out the isis fighters and took control of the dam.

But, in the months that followed, American officials inspected the dam and became concerned that it was on the brink of collapse. The problem wasn’t structural: the dam had been built to survive an aerial bombardment. (In fact, during the Gulf War, American jets bombed its generator, but the dam remained intact.) The problem, according to Azzam Alwash, an Iraqi-American civil engineer who has served as an adviser on the dam, is that “it’s just in the wrong place.” Completed in 1984, the dam sits on a foundation of soluble rock. To keep it stable, hundreds of employees have to work around the clock, pumping a cement mixture into the earth below. Without continuous maintenance, the rock beneath would wash away, causing the dam to sink and then break apart. But Iraq’s recent history has not been conducive to that kind of vigilance.

In October, Iraqi forces, backed by the United States, launched a sprawling military operation to retake Mosul, the largest city under isis control. The battle has sometimes been ferocious, with Iraqi soldiers facing suicide bombers, bombardments of chlorine gas, and legions of entrenched fighters. Although some Iraqi leaders predicted a quick success, it appears that the campaign to expel isis will be grinding and slow. And yet the biggest threat facing the people of northern Iraq may have nothing to do with who controls the streets.

In February, the U.S. Embassy in Baghdad issued a warning of the consequences of a breach in the dam. For a statement written by diplomats, it is extraordinarily blunt. “Mosul Dam faces a serious and unprecedented risk of catastrophic failure with little warning,” it said. Soon afterward, the United Nations released its own warning, predicting that “hundreds of thousands of people could be killed” if the dam failed. Iraq’s leaders, apparently fearful of public reaction, have refused to acknowledge the extent of the danger. But Alwash told me that nearly everyone outside the Iraqi government who has examined the dam believes that time is running out: in the spring, snowmelt flows into the Tigris, putting immense pressure on the retaining wall.

If the dam ruptured, it would likely cause a catastrophe of Biblical proportions, loosing a wave as high as a hundred feet that would roll down the Tigris, swallowing everything in its path for more than a hundred miles. Large parts of Mosul would be submerged in less than three hours. Along the riverbanks, towns and cities containing the heart of Iraq’s population would be flooded; in four days, a wave as high as sixteen feet would crash into Baghdad, a city of six million people. “If there is a breach in the dam, there will be no warning,” Alwash said. “It’s a nuclear bomb with an unpredictable fuse.”

Since civilization dawned in the Middle East, five and a half thousand years ago, the region’s politics and economy have centered on its two great rivers, the Tigris and the Euphrates. The rivers, which enter Iraq from the north and converge two hundred and fifty miles south of Baghdad, form an extraordinarily fertile valley in an otherwise dry part of the world. For centuries, populations flourished by tilling the rich alluvial soil left behind each spring by floodwaters receding from the plains between Baghdad and the Persian Gulf. But the rivers also wreaked havoc, delivering too much water or not enough, and the settlements on their banks lurched between periods of drought and flood.

In the nineteen-fifties, governments in the region moved to assert greater control over the rivers with aggressive programs of dam construction. Dams regularize the flow of water, discourage floods, and, by storing water in reservoirs, minimize the impact of droughts. They also give whoever controls them power over the flow of water downstream, rendering other countries vulnerable.

In 1975, when both Syria and Turkey were completing dams on the Euphrates, and the reservoirs behind them began to fill, the river downstream dried up, forcing tens of thousands of Iraqi farmers to abandon their land. “You could walk across the Euphrates, it was so dry,” an Iraqi engineer who worked on the Mosul Dam told me. The same year, Turkey began surveying sites for another dam, just north of the border it shares with Iraq, on the Tigris River. Iraqi officials feared that, during the months or years when the new dam’s reservoir was being filled, many thousands of acres of farmland would have to be abandoned.

At the time, Saddam Hussein’s government was launching a hugely ambitious program of infrastructure development. The regime was awash in money; a previous government had nationalized the oil industry and renegotiated its relationships to the Western companies that had once controlled it. Saddam decided to build dams on both the Tigris and the Euphrates.

Western specialists began making surveys to find the most favorable site, but few places had the right topography for a reservoir: low-lying land, preferably surrounded by mountains. The geology presented even greater problems. Water in dam reservoirs creates tremendous pressure, and only solid rock can stop it from leaking underneath the dam. The surveys revealed a multilayer foundation of anhydrite, marl, and limestone, all interspersed with gypsum—which dissolves in contact with water. Dams built on this kind of rock are subject to a phenomenon called karstification, in which the foundation becomes shot through with voids and vacuums. According to former Iraqi officials who worked on the project, successive teams of geologists reached the same conclusion: no matter where they looked, the prevalence of gypsum would make maintaining a dam difficult.

The government settled on a site north of Mosul, which had the largest potential reservoir of any of the locations the geologists had scouted. “The engineers wanted to show Saddam that they could build something huge,” an Iraqi official who had worked on the dam told me. The location also offered the opportunity to open up tens of thousands of acres north of the dam to irrigation and agriculture, in a series of projects the government called al-Jazeera, or “the peninsula.”

In 1981, Saddam ordered the construction to begin—urged on, according to another former senior Iraqi official, by the military situation. (The official, who lives in Baghdad, spoke to me on condition of anonymity, fearing that he would lose his pension if he spoke out.) A year before, Saddam had launched a huge invasion of Iran, hoping to seize its oilfields and possibly to overthrow its government. But the Iranians pushed back, and the war became a bloody stalemate, with fighting concentrated along the border, near the southern city of Basra.

As the Iraqi soldiers dug in, they were vulnerable to the fluctuations of the Tigris. In 1954 and again in 1969, floods had swept through the south of Iraq, separating Basra from the rest of the country. “Historically, when there is above-average flooding on the Tigris, southern Iraq becomes one large lake,” the retired official told me. Iraq’s leaders feared that they were due for another flood, which would strand the Army. “It was of the utmost importance to begin construction of the dam as quickly as possible,” the official said.

The decision to build the dam started a decades-long argument over who is responsible for the looming disaster. Nasrat Adamo, a former senior official at the Iraqi Ministry of Irrigation, told me that a consortium of Swiss firms hired to oversee the process assured government officials that the gypsum problem could be managed. “We listened to the top experts,” he said. “Everybody agreed that this would not be too serious.” Adamo remains bitter. “The Iraqi government—in a way, I think they were cheated,” he told me. But other people who were involved in building the dam argued that the Iraqis should have been more cautious: the Swiss explained clearly that the site was problematic, and geologists working in the area had raised concerns for decades. They also noted that Soviet and French companies bidding on the project had asked for further surveys and been told that there wasn’t time. Iraqi officials were terrified of disappointing Saddam. Adamo told me that the Minister of Irrigation feared for his life: “If the dam failed, he would be hanged.”

The dam was built in three years, largely by workers from China. Today, a stone memorial on top of the dam commemorates nineteen Chinese nationals who died during its construction; the memorial, inscribed in English and Chinese but not in Arabic, does not give the cause of their deaths. Alwash, the Iraqi-American hydrological engineer, told me that, in Iraq, when laborers fell into wet cement during large infrastructure projects, it was common for the work to carry on. “When you’re laying that much cement on a dam, you can’t stop,” Alwash said. In 1985, the reservoir filled up, and the structure—named the Saddam Dam—began holding back the Tigris.

Shortly after the dam went into use, Nadhir al-Ansari, a consulting engineer, made an inspection for the Ministry of Water Resources. “I was shocked,” he told me. Sinkholes were forming around the dam, and pools of water had begun bubbling up on the banks downstream. “You could see the cracks, you could see the fractures underground,” Ansari said. The water travelling around the dam, known as “seepage,” is normal in limited amounts, but the gypsum makes it potentially catastrophic. “When I took my report back to Baghdad, the chief engineer was furious—he was more than furious. But it was too late. The dam was already finished.”

To control the erosion, the government began a crash program of filling the voids with cement, a process called “grouting.” Meanwhile, Iraqi officials rushed to build a second dam, near a town called Badush, which could help prevent flooding in case the Mosul Dam collapsed. By 1990, just six years later, the new dam was forty per cent complete. Then Saddam sent his Army into Kuwait, sparking the Gulf War, and he ordered all the earthmoving equipment stripped from the Badush site and sent to the front lines. When the United States and its allies arrived to expel the Iraqis from Kuwait, they bombed all the equipment. After the war, inspectors from the International Atomic Energy Association discovered stockpiles of nuclear materials near Badush, apparently part of Saddam’s secret weapons program. The U.N. imposed economic sanctions on Iraq, impoverishing the country for a decade. Work on Badush never resumed. “Nobody wanted to go anywhere near the place,” Adamo told me. “This is the story of Iraq.”

When the Americans invaded in 2003, they discovered a country shattered by sanctions. Power plants flickered, irrigation canals were clogged, bridges and roads were crumbling; much of the infrastructure, it seemed, had been improvised. The U.S. government poured billions of dollars into rebuilding it, and in 2006 the U.S. Army Corps of Engineers began several assessments of the Mosul Dam. The first report was dire, predicting “mass civilian fatalities” if it failed. “In terms of internal erosion potential of the foundation, Mosul Dam is the most dangerous dam in the world,” it said.

Iraqi officials were publicly skeptical, but, under pressure from the Americans, they agreed to lower the maximum depth of the reservoir by about thirty feet, to take pressure off the dam wall. At the same time, American officials also began urging Iraq to modernize the equipment used to reënforce the foundation. In 2011, the Iraqi government chose an Italian engineering company, Trevi S.p.A., to begin a restoration, but the discussions broke down. A spokesman for Trevi told me he didn’t know why. A senior American official who has spent years working in Iraq confided that the deal may have stalled after Trevi refused an Iraqi demand for a kickback. “It was too big for the Italians to make,” the official told me.

In November, 2015, Mohsen al-Shammari, then the Minister for Water Resources, told reporters that there was no chance that the dam would collapse: “Whoever is saying it’s about to collapse is only talking.” Shammari is a follower of Moqtada al-Sadr, the fiery cleric whose soldiers fought the United States during the occupation. Sadr’s followers refuse to meet with American officials, and so, until a new water minister, Hassan al-Janabi, took office earlier this year, no Iraqi minister responsible for the Mosul Dam had spoken to an American official in five years. Even Janabi, who American officials say is fully aware of the problems at the dam, dodged the issue when I asked about it this summer. “I have not inspected the dam personally, so I cannot say for sure if there are any problems there,” he said. “Call me after I have gone there and inspected it.”

In private, some Iraqis pose conspiracy theories. “I know a lot of Iraqis who think this is just a big psyops operation by the U.S. government—senior officials, not just Iraqis on the street,” a former American official told me. Part of the problem, he argued, is a tradition of inertia, begun during Saddam’s dictatorship, in which officials live in fear of being penalized for taking initiative. “Iraqis will ignore the problem until the day the dam collapses,” he told me. “I’ve seen it over and over and over again. If the boss says there’s no problem, then there is no problem. And the day there is a problem, it’s, like, ‘Help!’ ”

Riyadh al-Naemi, the dam’s director, looks like a holdover from the Baathist era. He wears a stout mustache, talks like a technocrat, and starts answering a visitor’s questions before he’s finished asking. Naemi has spent his career at the Mosul Dam; he was a young engineering graduate when it opened, and he remembers the day Saddam paid a visit, shortly after the Iran-Iraq War ended. Naemi has heard all the predictions of the dam’s imminent demise. “Sure, we have problems,” he says. “But the Americans are exaggerating. This dam is not going to collapse. Everything is going to be fine.”

Naemi told me that some American officials had come to him earlier this year to warn that the dam was going to break, and confronted him with satellite photos that showed water from the reservoir seeping through the sides of the dam. “I told them it was not important,” he said. “I explained to them that there was no problem—and they agreed with me.” The senior American official, frustrated at the years of inaction, told me that the Americans were not persuaded by Naemi: “He is not going to tell us the sky is falling. We shared the data that showed the risks of the dam, and it’s terrifying.”

The potential disaster has presented American officials with a public-relations quandary: the people they are trying to help won’t publicly concede that there’s a problem. In response, U.S. officials have gone silent. It took me more than a hundred phone calls, e-mails, and visits before a single American official was granted permission to speak to me on the record; even then, three other State Department officials listened in on the conversation. “We don’t want to publicly embarrass the Iraqis,” the senior American official told me.

A walk around the Mosul Dam gives you a sense of its scale and its problems. Four massive towers, part of the hydroelectric system, mark the western end. To the north is the reservoir, a deep-blue pool reaching to the gorge’s walls, miles away; to the south, the Tigris continues its long meander to the Persian Gulf. Along the edges of the dam, little springs spurt from the ground. Here and there are gauges and cameras, part of a system that collects real-time information—water pressure, temperature, chemistry—that the U.S. Army Corps of Engineers monitors around the clock.

At the bottom of the wall, where the Tigris gushes out, are two control gates, which allow water to be drained from the reservoir quickly, in case heavy rainfall or snowmelt builds up pressure on the dam wall. When I visited, in September, one of the gates was broken: stuck shut. The controllers have resorted to the working gate at least four times since isis was driven away from the dam. The final safety valve is a spillway—three hundred feet wide, half a mile long—that the dam’s controllers can throw open to prevent an imminent breach.

The work of maintaining the dam is performed in the “gallery,” a tunnel that runs inside the base, four hundred feet below the top. To get there, you enter through a portal near the river’s edge and walk down a sloping corridor into the center of the dam. The interior is cool and wet and dark. It feels like a mine shaft, deep under the earth. You can sense the water from the reservoir pressing against the walls.

Inside the gallery, the engineers are engaged in what amounts to an endless struggle against nature. Using antiquated pumps as large as truck engines, they drive enormous quantities of liquid cement into the earth. Since the dam opened, in 1984, engineers working in the gallery have pumped close to a hundred thousand tons of grout—an average of ten tons a day—into the voids below.

Up close, the work is wet, improvisatory, and deeply inexact. Gauges line the walls of the gallery, programmed to detect changes in pressure; water seeps through cracks in the floor. Ordinarily, the pressure is much higher on the upstream side—because the water is pressing against the dam wall. If the pressure readings on the two sides of the gallery begin to converge, water is probably passing underneath. “That means there’s a leak,” Hussein al-Jabouri, the deputy director of the dam, said, waving at a gauge.

Like his boss, Jabouri has worked at the dam since he was a young engineering graduate. Now, he told me, he is as sensitive to the dam’s changes as the electronic gear buzzing around him. Jabouri gave a signal—“Come”—and a crew of engineers wheeled one of the giant pumps into position. At his feet, all along the gallery floor, were holes that serve as guides for the industrial drills the engineers use to probe the voids.

At Jabouri’s command, the engineers began pushing a long, narrow pipe, tipped with a drill bit, into the earth. The void they were hunting for was deep below—perhaps three hundred feet down from where we were standing. After several minutes of drilling, a few feet at a time, the bit pushed into the void, letting loose a geyser that sprayed the gallery walls and doused the crew. The men, wrestling the pipe, connected it to the pump. Jabouri flicked a switch, and, with the high-pitched whine of a motorcycle engine, the machine reversed the pressure and the grout began to flow, displacing the water in the void. “It’s been like this for thirty years,” Jabouri said with a shrug. “Every day, nonstop.”

When I visited, only four grouting machines, instead of the usual eleven, were in use. The engineers operating them can’t see the voids they are filling and have no way of discerning their size or shape. A given void might be as big as a closet, or a car, or a house. It could be a single spacious cavity, requiring mounds of grout, or it could be an octopus-like tangle, with winding sub-caverns, or a hairline fracture. “We feel our way through,” Jabouri said, standing by the pump. Generally, smaller cavities require thinner grout, so Jabouri started with a milky solution and increased its thickness as the void took more. Finally, after several hours, he stopped; his intuition, aided by the pressure gauges, told him that the cavity was full. “It’s a crapshoot,” Alwash told me. “There’s no X-ray vision. You stop grouting when you can’t put any more grout in a hole. It doesn’t mean the hole is gone.”

Theoretically, it’s possible that all the voids underneath the Mosul Dam could be filled—that all the gypsum could be replaced with grout. “Not in our lifetimes,” an Army Corps of Engineers specialist told me. In the meantime, he said, “there are just enormous quantities of gypsum that are washing away.”

When isis fighters took the dam, in 2014, they drove away the overwhelming majority of the dam’s workers, and also captured the main grout-manufacturing plant in Mosul. Much of the dam’s equipment was destroyed, some by isis and some by American air strikes. The grouting came to a standstill—but the passage of water underneath the dam did not.

Iraqi and American officials are reluctant to discuss how long the grouting was suspended. Naemi, the dam’s director, maintained that it stopped for less than three weeks, while the battle for the dam was raging. American officials said they weren’t sure. Jabouri, the deputy director, told me that work had ceased entirely for about four months. Adamo, who said that he’d been in regular contact with the engineers at the dam, told me, “The grouting work stopped for eighteen months.”

It’s one of the ironies of Iraq’s political situation that the dam’s turbines still provide electricity to Mosul, which is now under isis control; intelligence reports indicate that isis has earned millions of dollars by taxing the electricity. After the peshmerga captured the dam two years ago, Kurdish officials intended to shut down the turbines, but American officials told them that this would add more water to the reservoir, making the dam more likely to burst. So isis continued to profit from the dam. “We wanted to strangle them, but we weren’t allowed,” a Kurdish official told me.

When the dam was recaptured, American engineers and scientists worried that the lapse in grouting had hastened the erosion of the dam’s foundation. Using satellite photos and data from gauges around the dam, they tried to assess its condition. According to a U.S. Army Corps of Engineers report, numerous voids had opened up below the dam—as much as twenty-three thousand cubic metres’ worth. “The consensus was that the dam could break at any moment,” John Schnittker, an economist who has been working on water issues in Iraq for more than a decade, said.

In the language of hydraulic engineering, the process eroding the foundation is known as “solutioning.” If that problem is not addressed, what happens next is “piping”: water begins to travel between the voids, moving horizontally beneath the dam. To illustrate, American engineers have devised a triangular chart. The process begins, at the apex, with solutioning, advances through cavity formation and piping, and ends with core collapse and, finally, dam breach—like a Florida sinkhole opening up, unannounced, beneath a shopping center. Engineers jokingly refer to the chart as the “triangle of death.” Schnittker told me, “Once piping begins, there is no going back. In twelve hours, the dam is gone.”

In 2010, an Iraqi graduate student commissioned a bathymetric survey of the reservoir floor, which is more than a hundred and sixty feet underwater. The survey showed a surface pockmarked with sinkholes, some of them sixty-five feet wide. “The danger is that the cavities underneath the dam will become much, much larger,” Adamo, the former deputy director of dams, told me.

In January, a team of American scientists reported that a thirty-metre-wide block on the western side of the dam had tilted, with one end sinking into the earth a tenth of an inch. (The State Department has refused to make the report public.) It was the fourth time the dam had moved since November, 2015. To engineers, uneven movement of a dam means that the ground underneath may be falling away; the uneven pressure could ultimately cause a breach.

Naemi, the dam’s overseer, said that the dam was merely “settling” into the earth. But most dams stop settling within a few months after they are built. Outside experts, including Ansari, told me that for the dam to move that much was highly irregular. “That’s more than it’s moved in thirty years,” he said. Alwash, the Iraqi civil engineer, told me, “Something has changed. The underlying soil is readjusting itself because of the voids.”

A second report, also kept from the public, was equally alarming. Like the first, it concluded that sections of the dam were moving unevenly, that water was passing through the foundation rapidly, and that water downstream contained high concentrations of dissolved gypsum—evidence of large voids. A chart compared the relative chances of collapse of a number of dams worldwide, and the likely death toll. A small number of dams were grouped toward the middle of the chart, indicating a moderate level of risk; the Mosul Dam stood by itself, nearly off the chart. “No dam in the world has all the conditions for imminent failure, except the dam in Mosul,” Adamo said.

In the nineteen-seventies, the U.S. government built a dam on the Snake River in Idaho, atop a foundation of deeply fractured layers of basalt and rhyolite. As in Mosul, experts expressed concerns but decided that aggressive grouting would allow the dam to function normally.

The Teton Dam opened in the fall of 1975; the following June, cracks appeared in the main wall, and water from the reservoir began to leak through. Within hours, the cracks spread, the dam disintegrated, and a wall of water poured forth. The wave swept aside everything in its path, including two towns, at least eleven people, and thousands of cattle. The water knocked loose a large clutch of felled trees from a nearby forest, which washed downstream and crashed into a gasoline storage tank. The leaking gas burst into flames, and the fire, as it spread, destroyed several hundred homes that had been spared by the flood.

The U.S. Embassy’s report on the Mosul Dam envisions a similar scenario, magnified by the dam’s greater size and the densely populated areas downstream. A “tsunami-like wave” would rush through Mosul, carrying away everything in its path, including bodies, buildings, cars, unexploded bombs, hazardous chemicals, and human waste. The wave would almost certainly catch most of the people trying to outrun it. Residents of Mosul, scrambling on foot and by car through a citywide traffic jam, would need to travel at least three and a half miles to survive. In less than an hour, those who remained would be under as much as sixty feet of water.

With Mosul and other nearby villages occupied by isis, an orderly evacuation would be unlikely; the prospect of large numbers of people fleeing cities under isis control would pose its own security challenges. “Some evacuees may not have freedom of movement sufficient to escape,” the report said. An inland tidal wave could displace the 1.2 million refugees now living in tents and temporary quarters in northern Iraq, adding to the chaos.

The wave, the Embassy’s report predicted, would move rapidly through the cities of Bayji, Tikrit, and Samarra, wiping out roads, power stations, and oil refineries; damage to the electrical grid would probably leave the entire country without power. At least two-thirds of Iraq’s wheat fields would be flooded.

South of Samarra, residents would likely have to get farther away to avoid flooding, since the land begins to flatten out, making the floodplain wider. Shallow floods, the State Department said, could not be ignored. “Less than six inches of moving water is strong enough to knock a person off his feet,” the statement said.

Within four days, the wave would reach Baghdad, depositing as much as sixteen feet of water in many areas of the city, probably including the airport and the Green Zone, the site of government buildings and most of the embassies. The report said the majority of the city’s six million residents would face Hurricane Katrina-like conditions: people forced from their homes, with limited or no mobility and no essential services.

The Iraqi government—embattled, paralyzed, ineffectual—seems highly unlikely to carry out meaningful evacuations or large-scale relief efforts in the event of a breach. “The sheer scale of a catastrophic outburst of the dam would overwhelm in-country capacities to respond,” the U.N. report said. Adamo, the former official, scoffed at the idea that the government could save anyone. “They have no plan,” he said. American officials, emphasizing the practical option of “self-evacuation,” have urged the Iraqis to place early-warning sirens along the Tigris. Thus far, two have been installed. “They’re really, really loud,” the senior American official told me; they can be heard for miles. Still, as people flee, the sick, disabled, and elderly would likely be left behind. With the Baghdad International Airport flooded, meaningful relief from outside the country might be days away. The U.N. predicted that most of the population affected by the flood would not receive any assistance for at least two weeks, and probably much longer. About four million Iraqis—an eighth of the country’s population—would be left homeless.

By the time the flood wave rolled past Baghdad and exhausted itself, as many as one and a half million people could be dead. But, some experts told me, the aftermath would prove even more harrowing. “I am not really worried about the dead—because they’re dead,” Alwash said. “What worries me is everyone else. How do you feed six million people in Baghdad when it’s flooded? How do you give them electricity? Where do they go?”

Nadhir al-Ansari, the engineer who made the first inspection of the Mosul Dam, now lives in Luleå, Sweden. Adamo, the former chief engineer, lives in Norrköping, about six hundred and fifty miles to the south. The two remain obsessed with the dam, haunted by decisions made more than thirty years ago. They confer on the phone daily and get together to discuss the situation; they sometimes reach out to engineers who work at the dam. Adamo keeps an up-to-date maintenance log in his office in Norrköping. Neither he nor Ansari is optimistic that the Iraqi government will be able to solve the problem in time. “I am convinced the dam could fail tomorrow,” Adamo said.

Perhaps the simplest solution is to scrap the dam entirely and make a deal to lease Turkish dams north of the border. But the political instability in the region makes such an accord practically impossible. Another option is to re-start construction of the half-completed dam at Badush, but the smaller reservoir would likely require tens of thousands of acres of land to be removed from cultivation. A third option, which has lately gained currency, is to erect a “permanent” seal of the existing dam wall—a mile-long concrete curtain dropped eight hundred feet into the earth. This would cost an estimated three billion dollars. The Iraqi government—nearly paralyzed by internal conflicts—seems unlikely to impose a solution anytime soon.

Early in 2016, under American prodding, the Iraqis reopened negotiations with Trevi S.p.A., the Italian firm. In September, a team of engineers, hired at a cost of three hundred million dollars, arrived at the dam to perform a crash repair job. Their main task is to install updated equipment, designed to fill the voids beneath the dam more precisely, and to repair the broken control gate. Under the contract, the Italians will do the grouting for a year, and then leave the equipment with their Iraqi counterparts. The engineers say that they are confident they can prevent the dam’s foundation from washing away. But Pierluigi Miconi, Trevi’s project manager, told me that some of the voids may require tens of thousands of gallons of grout. In some cases, he said, it may take days to fill a single void. “This is an urgent project,” he said.

Last year, Alwash, the Iraqi-American civil engineer, was told by an official of the European Union that the dam is most susceptible to failure in the spring, when the snow melts and the Tigris is at its highest. The officials who first argued for the construction of the Mosul Dam, back in the eighties, were motivated by similar concerns about snowmelt—and they were proved right. In 1988, there was a huge melt, which would almost certainly have flooded the southern marshes if the dam had not contained the worst of it. Last spring, the Iraqi government prepared by lowering the maximum water level in the reservoir, to ease severe pressure on the dam wall. This year, such a precaution could dramatically lessen the number of people at risk—to about three hundred and sixty-four thousand.

The Trevi engineers, scrambling to keep the dam functioning, are operating in a militarized environment. Hundreds of Italian and Kurdish soldiers patrol the area, on alert for an attack by isis. In September, the Italian media reported that isis fighters were preparing an operation to recapture the dam. The following month, Kurdish forces fired a missile at a team of isis commandos who were approaching with a load of explosives.

For local residents, the threat of imminent violence has outweighed the threat from the dam. In Wanke, a small farming community about three miles downstream of the dam, isis positions are visible from the riverbank. When I visited, I found Mohammed Nazir, a Kurdish farmer, irrigating his field. For years, he told me, Wanke was a mixed Arab-Kurdish community. But when isisfighters swept in, during the summer of 2014, many of his Arabic neighbors stepped forward to help the invaders. “They told us, ‘This is not a Kurdish town anymore,’ ” Nazir said. “It was humiliating. They started ordering us around. I knew their children. I went to their weddings. They betrayed everything in life.”

Nazir and his family escaped to a nearby village, where they lived with relatives for a year and a half before isis was expelled from Wanke. When the family moved back, Nazir found that his Arab neighbors had fled with the retreating invaders. “They are not welcome back here,” he said.

Nazir knows that, if the dam fails, Wanke could be under sixty feet of water in a matter of minutes. But, he told me, neither he nor anyone else in the village thinks much about it. People in his part of the world are accustomed to having their lives upended. “We survived Saddam, we survived isis, and we will survive the Mosul Dam,” he said.

Author: Dexter Filkins

Source: newyorker.com