The Alvin Sea Serpent is called such due to it being seen by witnesses aboard the Alvin, a mini-submarine. It was seen during October of 1969 during a dive off the coast of the Bahamas. The submarine's driver, Marvin McCamis, was one of the witnesses of the creature. McCamis' sighting was documented in Charles Berlitz's 1977 book Without a Trace.

“We were down about 5000 feet and then I went down into a crevasse about 300 feet deeper under a slight outcrop. We went deeper because the cable we were following spanned the crevasse. It was right there that I spotted it. The first thing I noticed was the movement. I thought we were moving along the cable and checked for drift but found that the sub was stationary and that it was the object that was moving. It then occurred to me that perhaps it was a utility pole, especially because of its thick shape. I swung the sub in an arc to get a better view along the cable or pole or whatever it was, when I was astonished to see a thick body with flippers, a long neck, a snakelike head with two eyes looking right at us. It looked like a big lizard with flippers - it had two sets of them. Then it swam upwards with its back turned before we could get the cameras angled. They were set to photograph 15 to 25 feet in front of the submarine and the thing had already swum out of the camera angle but was still around. I didn't like the way things were happening, so I came up. I couldn't believe what I was seeing but I didn't want to hang around.”