In a small coastal fishing village called Noyo in northern California, the residents are set to celebrate their annual salmon festival. The festival has been on the decline of late because the fish population has dwindled, leaving the town suffering  Doug McClure plays a fisherman and trusted community leader named Jim Hill (Doug McClure), doing what he can to keep harmony among his neighbors. Vic Morrow is the town's more aggressive type, twisting whatever arms necessary to get a company to establish a cannery in town. Anthony Pena is among the Native Americans protesting the cannery planning to exploit his tribe's land.

The corporation has been experimenting with ways to escalate the growth of fish in the area. Ann Turkel is a scientist named Dr. Susan Drake who led the experiments, which involved tinkering with salmon DNA so they'd grow large and increase spawning activity. However, the experiment goes awry after prehistoric coelacanths begin to consume these genetically altered salmon. Their offspring evolves quickly into humanoid sea creatures that emerge out of the ocean, attacking landlubbers with an overwhelming desire to feed on mammals and procreate with human women.

Directed by Barbara Peeters for Roger Corman's New World Pictures.