Since Venice is built on a lagoon, the canal waters are brackish, meaning that they are a mix of salt and freshwater. There is heavy chemical runoff from the industrial area in Porto Marghera, as well as waste from the rivers on the west side of the city. Throughout the year over 600 cruise ships anchor in Venice.

Yes, the water in the Venice canals is salty (brackish) because the canals are part of the Venetian Lagoon, which is directly connected to the Adriatic Sea. The lagoon is a semi-enclosed body of water where saltwater from the sea mixes with freshwater flowing in from several rivers (like the Brenta and Sile). This creates a "polyhaline" environment, meaning it is significantly saltier than a river but slightly less salty than the open ocean. Because the canals are subject to the tides, the water is constantly circulating; during high tide (Acqua Alta), fresh saltwater from the Adriatic rushes into the city, while during low tide, the water recedes back into the lagoon. This salinity is actually a major engineering challenge for the city, as the salt penetrates the porous bricks and mortar of the historic buildings, causing them to slowly erode through a process called "capillary rise." In 2026, the MOSE barrier system—a series of mobile gates—helps regulate the water levels during extreme tides, but the fundamental chemistry of the canals remains salty, supporting a unique ecosystem of salt-tolerant crabs, mussels, and algae that locals have observed for centuries.