Octaman (1971) on Netflix

Plot summary

A research team working near a remote Mexican fishing village traces radiation in the local waters and captures a small octopus-like creature that can crawl on land. Rick Torres takes the findings back to the States hoping for more funding, and when the scientific establishment shows little enthusiasm, he agrees to let a circus owner, Johnny Caruso, exhibit the creature as a carny act. In Torres's absence, a humanoid octopus, Octaman, appears at the camp. Davido, a young man from the nearby village, tells the group that a local legend of a creature part man and part sea serpent is real, and offers to lead them to the lake where it is said to live.