The Fraggle Pond seen drained during Pa Gorg's daily bath.
The Fraggle Pond is located in the Great Hall of Fraggle Rock and directly below the well in the Gorgs' Garden. It serves as a public swimming pool, and is the location of Red's many swimming lessons and diving exhibitions.
Fed by Doc's plumbing, it empties every day when Pa Gorg takes a bath, whereupon the Pipebangers (led by Archbanger Fraggle) bang on Doc's pipes, causing him to turn on more water and refill the pond.
According to a sketch seen in the bonus features of the Fraggle Rock: Complete First Season DVD, the pond feeds an underground river which leads to Doc's town's water supply. The Doozers have built a hydroelectric plant to harness the river's energy.
Red Fraggle's job is to "clean" the Fraggle Pond (by diving and swimming in it).