Iceland has over 20 lakes larger than 10 km2 (4 sq mi), and at least 40 others varying between 2.5 and 10 km2 (1 to 4 sq mi) in size. This list also includes a few smaller lakes and ponds that are considered notable (for example Tjörnin in Reykjavik). The figures for many of the smaller lakes are unreliable. Also, some larger lakes vary considerably in size between years or seasons or, for the reservoirs, according to the needs of power plants. Some power plant reservoirs may not be present despite being larger than listed lakes.