U.S. officials are warning that the largest dam in Iraq is in danger of collapsing. They say flooding caused by the collapse would kill a half million people in the nearby city of Mosul. But the manager of the dam says even though there are problems, the dam will not fall down. VOA's Deborah Block visited the Mosul Dam and has a report.

But the U.S. Army Corps of Engineers says Mosul dam should be shut down, calling it is the most dangerous dam in the world because of erosion problems. They warn that the wall of the dam holding back the Tigris River could collapse at any time.

Earlier this year, the top American commander in Iraq, General David Petraeus, along with the U.S. Ambassador in Baghdad, Ryan Crocker said a flood would not only affect Mosul but devastate cities farther south, including Baghdad.

But Iraqi government spokesman Ali al-Dabbagh does not agree with the reports and says Mosul Dam is in good condition and not in danger.

Abdulkhalik Thanoon Ayoub, is an engineer and manager of the dam. He says there is no cause for alarm.

"This is the best place to build a dam, except for one factor, and that is the geology," he said. "My office is on the downstream side of the dam and I can say with confidence that I am not worried."

But he agrees that the three-kilometer structure has a major problem because it was built on top of gypsum, a mineral that dissolves in water. Over time water flowing over the gypsum is causing cracks and holes that are constantly being grouted with concrete material to prevent the dam from collapsing. Ayoub says this solution has worked since the dam was built more than 20 years ago.

"We have no other choice," he said. "We have to perform this grouting continuously to reinforce the foundation, and at the same time, we have to find a permanent solution."

It is not clear why the dam was constructed in an unstable location since Iraqi engineers knew about the problem from the beginning. But it was built at a time when Saddam Hussein decided where many construction projects in Iraq would be located.

Contributing to the problem is a recent report by a U.S. oversight agency that says a $27 million American reconstruction project to improve the dam and grouting has been mismanaged and not led to significant improvements.

The U.S. Army Corps of Engineers is recommending building a second dam downstream as a backup. But Iraq's government is resisting the costly project and says it is not necessary. Ayoub says Iraq's Ministry of Water Resources is cautious, but open to suggestions, including those by the U.S. Army Corps of Engineers.

"Their report did not convince engineers with the Iraqi water resources ministry about their conclusion 100 percent, " said Ayoub. "We have invited specialized companies from Germany, Italy, and other countries [to help us], and we got encouraging news that there is a permanent solution."

Ayoub says one possibility is installing a vertical plane of cement that would stop the water from flowing across the gypsum and prevent it from deteriorating.

"It is an easy solution because you can start directly from the foundation, which would eliminate the movement of water," he said.

U.S. officials are urging Iraq to make the safety of the dam a national priority. They fear that if nothing is done soon, it will collapse and thousands of people will lose their lives.