Black Lake

The Black Lake(alternatively known as the Great Lake) is a large body of water located to the south of the castle. It is about half a mile in diameter and the Hogwarts plumbing network drains into it. It is home to a Giant Squid, Grindylows, and a colony of Merpeople. The Slytherin common room is beneath the lake, accessed through an entrance in the school dungeons. The Chamber of Secrets is also thought to be beneath the lake.