Lochjaw (Atari 2600)

You are searching for a fabulous treasure of diamonds that spilled from the hold of a sunken Spanish galleon. You dive into the murky darkness and enter the shark-infested maze of kelp. You accept the danger... the terrible man-eating sharks and the lurking menace of the Loch Ness monster who will pursue you relentlessly.

(a.k.a. Shark Attack)