Coral reef A fringing reef forms around an extinct volcanic island as the island and ocean floor subsides. As the subsidence continues, the fringing reef becomes a barrier reef and ultimately an atoll reef. Darwin predicted that underneath each lagoon would be a bedrock base, the remains of the original volcano. Subsequent research supported this hypothesis. Darwin's theory followed from his understanding that coral polyps thrive in the tropics where the water is agitated, but can only live within a limited depth range, starting just below low tide. Where the level of the underlying earth allows, the corals grow around the coast
Open-air Water Museum hall, a recreation area and an open-air cinema. There are many water channels on the site. Open-air Water Museum The Open-air Water Museum () is located in the city of Edessa, Central Macedonia, Greece. In the early 20th century there were many water-powered workshops in the city. In 1991 the Municipality of Edessa decided to improve and develop the Mills area, the Kannavourgio and the ‘Estia’ works, by establishing an open air, water-power museum, and creating recreation areas. The Open-Air Water Museum, which opened early in 2000, aims to acquaint visitors with the history of water-power from the workshops of