Hammersø
Hammersø, or Hammer Sø, is the largest lake on the island of Bornholm and the only tarn in Denmark. It is located in a valley in Hammeren, the northernmost point of the island. A narrow isthmus separates the lake from Opalsø, an artificial lake formed in a granite quarry which was closed in 1970.Geography
The lake is about long and wide, covering an area of, and reaches a maximum depth of. Its encatchment area is approximately, consisting of about 50% rocks, 25% forest and 25% cultivated land.Biology
