Diving is free but you do need permission to dive there from the National trust warden. Max depth is said to be 75 meters. with up to 20m viability, but there isn't much to see.
Half way down the west side is the pinnacle, A rope leads out to the top of the pinnacle which the drops to a depth of 50m. There used to be a gnome garden but this was removed by police divers after several deaths. There is also wreck of a Lancaster Bomber at the end of the lake but not much remains of this.