Kappa are legendary creatures; a type of water sprite found in Japanese folklore. However they are also considered to be a part of Cryptozoology, due to claims of sightings. It could be the Japanese giant salamander.
Kappa (河童), are creatures from Japanese folklore that are most of the times dangerously mischievous and brutally deadly, but can be obsessively polite and helpful at times. They are said to be really scary (unlike this picture haha, because we like.