To my my mind there's a much scarier, and grislier, shark scene in the Leonardo de Caprio film, 'The Beach'. If I remember correctly some western backpacker types set up a community on a remote beach by the Andaman Sea (?). Well, an island off Thailand anyway. One of the group goes swimming, in a beautiful clear lagoon, one day and a shark takes a huge bite out of him. He bleeds so spectacularly that I almost passed out! Also, if I remember correctly, he is far from any medical help, the wound becomes infected and he dies in agony. Altogether much more realistic and horrible than anything in Jaws.