Jaws (1975)
I always liked this one, though its PG rating is a bit deceiving (it’s another from before the PG-13 rating existed).
This movie gets graphic and gruesome — in the way only a movie about a giant carnivorous animal can.
It’s well paced, well acted, and absolutely terrifying at times. I was at the edge of my seat literally at least once.
I never liked the beach much anyway (too warm and sunny for me), but watching this movie when I was very young ensured I stayed as far away from the ocean as possible. Which got a bit difficult as my grandmother lived in Florida and I spent a few summers with her.
That said, I grew up around Lake Michigan and never worried too much about sharks there. I always assumed it was too cold (and not salty enough) for them and just cold enough for me.