"The lake did not seem to be deep. Soon it was more a question of fighting their way through reeds and mud than swimming, and at last they flopped, sodden, panting, and exhausted, onto slippery grass."
Harry Potter, Ronald Weasley, and Hermione Granger wade across the lake[src]

This lake is where Harry Potter, Ron Weasley, and Hermione Granger ended up after they escaped Gringotts on one of its own dragons. From there, the trio Apparated to Hogsmeade. The said dragon possibly resides in that area to this day.