Who are the Merpeople in the Harry Potter books?

The merpeople in the "Harry Potter" books are a race of intelligent, amphibious creatures that live primarily underwater. According to the books, they live in bodies of water throughout the wizard world, including a lake on the grounds of Hogwarts.

The merpeople who live near Hogwarts are taller than humans. They have gray skin, yellow eyes, sharp teeth and long, green hair. While the upper half of the merpeople's bodies is human in appearance, their lower halves resemble the tails of fish or dolphins. The creatures have a distinct language that sounds like a series of croaks when heard underwater.