A court issued arrest warrants last week for suspects including Venice Mayor Giorgio Orsoni. All denied any wrongdoing.
They are suspected of having engineered a complicated series of kickbacks in the more-than €5 billion project designed to protect the city with a flood barrier.
"The investigation has not ended with the arrest warrants," lead prosecutor Carlo Nordio said. "We are pursuing several investigative lines."
The kickbacks for Moses, a project started a decade ago to isolate the Venice Lagoon from the Adriatic Sea at high tides, involve large sums.
"The figures are stratospheric," Nordio said. Italian media reported the kickbacks may have taken €1bn, almost 20 per cent of the funds spent on the project.
"On Friday, we will pass an ad-hoc measure to fight corruption," Prime Minister Matteo Renzi said.