Østensjøvannet is a lake in Oslo, capital of Norway. It is well known for the wide variety of birds and other wildlife that can be found there. It is surrounded by the Østensjø borough. It is currently a wildlife preserve, though urban development posed a serious threat to the lake and its environs during the 1980s and early 1990s. Østensjøvannet ("Østensjø lake") takes its name from Østensjø farm, situated on the lake's east side. The name of the farm is in turn related to the lake, "Østensjø" literally meaning "east of the lake". So in effect, the name means "The east-of-the-lake lake".