It is the latest in a series of Italian bribery investigations involving high-profile public works projects.
Police confirmed Mayor Giorgio Orsoni had been arrested. One report said he was being investigated for alleged corruption, extortion and money laundering.
The arrests were the result of a three-year investigation that led to the arrest last summer of the head of the consortium building the ambitious but long-delayed system of so-called Moses barriers. Authorities say £16million was diverted abroad to bribe politicians.