Guam Marine Salamander is an aquatic cryptid reported from Guam.
In 2004, a cryptid sighting was posted on a Japanese cryptid enthusiast exchange forum.
According to the submitter, the experience occurred a long time ago, when he was snorkeling in Guam's waters, observing sea cucumbers. The contributor was surprised to see a strange creature while snorkeling and rushed to shore. The creature he saw resembled a giant salamander in appearance, had four limbs and a tail, and was similar in color to a sea cucumber.
It was thought that the identity could be a saltwater crocodile and was mentioned within the forum, but the poster never posted on the forum again, so it is not known if what he saw was a crocodile. Another possibility is that they misidentified the shark species, such as the tawny nurse shark.