Sværsvann is a lake in the southeast of Oslo

Oslo

Oslo is a municipality, as well as the capital and most populous city in Norway. As a municipality , it was established on 1 January 1838. Founded around 1048 by King Harald III of Norway, the city was largely destroyed by fire in 1624. The city was moved under the reign of Denmark–Norway's King...

, Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

. The lake drains off into the river Hobølelva

Hobølelva

Hobølelva is a river rising in Sværsvann in Oslo, until joining Lake Vansjø in Østfold. Hobølelva is the largest of the four tributaries of Vansjø, and flows into Vansjø at an average of 5.4 m³/s....

. The lake's surrounding areas are mostly residential. Sværsvann is a popular bathing place, and the name is believed to origin from "Sværd Vandet", which means "Sword Water", because a sword was once found at the bottom of the lake. The bottom water contains huge amount of salts, organic nutrition and hydrogen sulfid.