His report also included a letter to Nuri al-Maliki, Iraq's prime minister, from the US ambassador to Iraq and the chief US military commander, which said: "A catastrophic failure of the Mosul Dam would result in flooding along the Tigris river all the way to Baghdad."
The dam was completed in 1984, but it was built on soluble soils that move and create cavities under the dam and its banks. Those cavities must be grouted to prevent collapsing.
The US and the Iraqi government started work to improve the dam in 2005.
"There is no danger, and in the case of this dam, the government, through the Ministry of Water Resources in collaboration with experts, is tackling the problems"
Ali al-Dabbagh, Iraq government spokesman
The US government provided funds for short-term solutions to the dam's problems while an Iraqi ministry was responsible for implementing a long-term solution.
Twenty-one contracts worth $27m were awarded by the US government to provide the Iraqi administration with needed replacement and spare parts for grouting operations, assistance with the grouting programme and enhanced grouting to augment Iraq's efforts.
Among other things, the US contracts were supposed to provide for five grout-mixing vehicles, Bowen said. One mixer was built, two were partially built and two were not built.
"Our inspection turned up evidence of potential fraud," he told a congressional panel. That has been referred to his investigative department, Bowen said.
Ali al-Dabbagh, an Iraq government spokesman, played down the report, saying it was old. He said all dams undergo annual repairs, but the Mosul Dam was monitored 24-hours a day and had 25 teams doing grouting work on the foundations.
"There is no danger. And in the case of this dam, the government, through the Ministry of Water Resources in collaboration with experts, is tackling the problems," he said on Iraqi television.