The Bisenzio (Italian pronunciation: [biˈzɛntsjo]), archaically also Bisenzo, is a 49-kilometer-long river in the municipality of Cantagallo.

It flows through the city of Prato and the Santa Lucia weir and the hydroelectric dam in Madonna della Tosse.

The river is a tributary of the Arno arising from the southern side of the Tuscan-Emilian Apennines.

It flows to the lowland continuing towards Florence, passing through San Piero a Ponti village until it flows into the river Arno by the Pass of Ponte a Signa, after travelling 29 km in the plains.

The water transported from Bisenzio has a very important role that balances the progressive lowering of the bottom of the lake basin.