Julie Blair is an American vacationing at a seaside village in Mexico. She hears stories about a man-eating creature dwelling in the cove. She meets Dr. Baldwin, a marine biologist, and they fall for one another. The mysterious death of a diver inspires Julie to investigate, but Baldwin is very skeptical. She sees a giant amoeba rising from the ocean.

References:
https://en.wikipedia.org/wiki/Monster_from_the_Ocean_Floor