Among those detained was Giovanni Mazzacurati, the director until last month of the consortium that is building the long-delayed multi-billion-euro project, along with several current members of the consortium and contractors.
He is suspected of "distorting" public tenders for the construction and favouring particular companies, the police said in a statement.
One part of the investigation also focussed on shell companies used to produce receipts for work that was never carried out.
Financial police said that they staged dozens of raids in Venice and other parts of Italy and were investigating a total of around 100 people.
Venice began construction in 2003 of mobile barriers at the mouth of its lagoon to protect the city from rising sea levels and the phenomenon of "high water" caused by currents and tides which floods the city every year.
The project, known by its acronym as "Mose" (Moses) is costing around €5.4 billion and is scheduled for completion in 2014.
The barriers will lie on the sea floor and be raised on their hinges with air pressure to block the tidal flow if the waters rise.