Obviously, most people will (justifiably) choose Jaws (1975) as #1. It is not just my all-time favorite aquatic thriller but my all-time overall favorite movie.
but here are the other nine listed in this article. Any comments about the list or any to add that was missed?
https://ew.com/movies/best-aquatic-horror-movies/
Creature From the Black Lagoon (1954)
Piranha (1978)
Leviathan (1989)
Deep Rising (1998)
Deep Blue Sea (1999)
Dagon (2001)
The Shallows (2016)
The Shape of Water (2017)
Underwater (2020)