Hammersø

{{Short description|Lake in Bornholm Regional Municipality, Denmark}}

{{Infobox body of water

| name = Hammersø

| native_name =

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| other_name = Hammer Lake, Hammer Sø

| image = Opalsø and Hammersø (Bornholm).jpg

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| caption = Opalsø (right) and Hammersø (left) seen from Hammerknuden

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| location = Bornholm, Denmark

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| coordinates = {{coord|55|16|58|N|14|45|54|E|type:waterbody_region:DK|display=inline,title}}

| type = Tarn

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| length = {{convert|650|m}}

| width = {{convert|150|m}}

| area = {{convert|10.3|ha}}

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| max-depth = {{convert|13|m}}

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| pushpin_map = Denmark

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| pushpin_map_alt = Location of Hammersø in Denmark.

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Hammersø (English: Hammer Lake), or Hammer Sø, is the largest lake on the island of Bornholm and the only tarn in Denmark.{{cite web|url=http://www.studienet.dk/Opgaver/Hammers%C3%B8en--24294.aspx|title=Rapport: Hammersøen|language=da|publisher=Studienet.dk|access-date=2012-06-07}} 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.{{cite web|url=http://www.denstoredanske.dk/Danmarks_geografi_og_historie/Danmarks_geografi/Bornholm/Hammeren|title=Hammeren|language=da|publisher=Gyldendal|access-date=2012-06-07}}