Oslo occupies an arc of land at the northernmost end of the Oslofjord. The fjord, which is nearly bisected by the Nesodden peninsula opposite Oslo, lies to the south; in all other directions Oslo is surrounded by green hills and mountains. There are 40 islands within the city limits, the largest being Malm�ya (0.56 km/0.22 sq mi), and scores more around the Oslofjord. Oslo has 343 lakes, the largest being Maridalsvannet (3.91 km/1.51 sq mi). This is also a main source of drinking water for large parts of Oslo.
Although Eastern Norway has a number of rivers, none of these flow into the ocean at Oslo. Instead Oslo has two smaller rivers: Akerselva (draining Maridalsvannet, which flows into the fjord in Bj�rvika), and Alna. The waterfalls in Akerselva gave power to the first modern industry of Norway in the 1840, and later in the century, the river became the symbol of the stable and consistent economic and social divide of the city into an East End and a West End; the labourers' neighbourhoods lie on both sides of the river, and the divide in reality follows Uelands street a bit further west. River Alna flows through Groruddalen, Oslo's major suburb and industrial area. The highest point is Kirkeberget, at 629 metres (2,064 ft). Although the city's population is small compared to most European capitals, it occupies an unusually large land area, of which two thirds are protected areas of forests, hills and lakes. Its boundaries encompass many parks and open areas, giving it an airy and green appearance
