The Blue Lagoon in Abereiddy, Wales is a small oasis on the west coast of the United Kingdom. Originally a slate quarry, it was shut down in 1910. The mine was flooded (on purpose) by local fisherman who blasted a narrow channel in the seaward side of the quarry, which allowed the ocean to flood the pit and provide shelter for their boats. The fishing industry has all but disappeared from Abereiddy Bay, and these days the lagoon is more popular for swimming, diving and exploring than as a boat harbor.
Evidence of the industrial era still stands around the lagoon, and the remaining slate walls are popular diving platforms. Even though it was considered a small quarry, The Blue Lagoon is pretty deep —- 25 meters according to the Pembrokeshire National Park. The water is a recognizable green-blue hue, which gets its color from the mineral content of the submerged slate.