Sharks in Venice (2008) on Netflix

Plot summary

Archeologist David Franks and his girlfriend Laura come to Venice, where Venetian police are helping them look into the strange disappearance of David's father, who went missing while diving in the city. On the boat trip to the spot where they believe he was last seen, David spots what looks like the fin of a big shark cutting the water. When he looks again, nothing is there. David and another man, Rossi, put on wetsuits and scuba gear and descend into the canals. Something large attacks the pair, and David is bitten in the shoulder before he makes it into a cave.