It's easy to forget Hawaii when looking at American cryptids. When I was young, Hawaii was not a state. But back in the 1950s, some children reported a lake mermaid in Hawaii. She wasn't quite your conventional sort of Mermaid. The creature was sighted in Lake Wilson. She had hair like seaweed, long claws and was colored green. This must have been somewhat scary.
Lake Wilson (pictured below) is on the island of Oahu.