Lake Inarijärvi is the third largest lake in Finland. Its area covers 1,040 square kilometres. The outlet of Lake Inarijärvi, the Paatsjoki River, empties into the Varangerfjord on the Barents Sea. The water level in Lake Inarijärvi is 117–119 metres above sea level and is regulated at the Kaitakoski power plant of the Paatsjoki River in Russia.
Lake Inarijärvi is the second deepest lake in Finland after Päijänne Lake. The deepest point of Lake Inarijärvi is at the northern depression of Vasikkaselkä and measures 91.9 metres. For most part, however, Lake Inarijärvi is shallow.
Open lake areas in Lake Inarijärvi include Ukonselkä, Kasarinselkä, Sammakkoselkä Vasikkaselkä and Satepetäjänselkä. There are 3,318 islands in the lake, of which the largest are Kaamassaari, Mahlatti, Viimassaari and Roiro. The most famous islands are Hautuumaasaari (Graveyard Island) and Ukonsaari Island, which is a historical Sámi sacrificial site. On an island called Korkia Maura, there is an ice cave where ice usually does not melt even in summer. The lake has a vast network of wilderness huts.
There is plenty of Salmonidae in the lake: Atlantic salmon, trout, Arctic char, lake trout, whitefish, vendace, grayling – as well as other fish.