Europe > Norway

Lake Mjosa: The Largest Lake in Norway

lakeMjøsa
countryNorway
surface area365 km2
maximum depth449 m
average depth80 m
lake typeGlacial
length117 km
width15 km
catchment area16,680 km2
altitude109 m
volume30 km3
inflowsGudbrandsdalslogen
outflowsVorma
islandsHelgoya
shore length341 km
age10000
mixing typeDimictic
settlementsHamar, Gjovik, Lillehammer
residence time1,217 days
frozenDecember to March
originGlacial
average discharge277 m3 / sec.

Mjøsa Information and Facts

Lake Mjosa is the largest and 4th deepest lake in Norway. It is located in one of the most populated areas in the country, with the cities Hamar, Gjovik and Lillehammer on its shores. The lake’s name is old and probably means "the bright, shiny one".

Geographic Facts

The lake lies in a glacially modified structural depression. It is long and narrow, with a north-northwest to south-southeast axis, and is a link to the Lagen River (to the north) and the Vorma-Glomma River System to the south. A large part of its catchment area is made up of mountainous regions with gabbroic and granitic bedrock. The lake has a total coastline of 273 kilometers, of which more than 30% are built up. The shores are mainly dominated by rolling agricultural areas, with some of the most fertile grain lands in Norway.

The lake is located in the southern part of Norway, 100 kilometers north of Oslo. Before the construction of the railways it used to be an important transportation route. Today there’s much less traffic on the lake, with only minor leisure boats and the Skibladner steamship floating on its waters.

The main island on the lake is Helgoya, which is surrounded by other small islets. The most interesting is Steinsholmen, on which one can find ruins of a Middle Age Citadel.

Hydrology

The lake’s main tributary is the Gudbrandsdalslagen, which arrives in the northern part of the lake and through which flow 75% of the lake’s waters. Mjosa’s main outflow is the Vorma River, which is located on the south and was dammed in 1858, 1911, 1947 and 1965. The damming raised the water level by approximately 3.6 meters. Melting snow and ice coming from the mountains ensures a high flow during the summer months. 60% of annual water flow occurs from June to August. The lake is used as a reservoir for hydroelectric power generation.

During the last 200 years more than 20 floods have been documented, which have added 7 meters to the water level. Several of these floods have inundated the city of Hamar.

The lake was endangered in the ‘70s after a sudden boom in algae. But because of the quick action of locals, a program was completed in 1980 to eliminate the inflow of untreated sewage. This led to the improvement of the quality of nearby rivers, and consequently the quality of Lake Mjosa.

Recreation, Leisure and Events

Approaching the lake is easy, since the main trine line, Dovrebanen, between Oslo and Trondheim, runs along the eastern shore and makes stops in Hamar and Lillehammer. From the south the European Route E6 approaches the lake, running along its eastern shore until the Mjosa Bridge connects Moelv on the East with Biri on the West.

Around twenty species of fish inhabit the lake, with pike, European perch, common roach, grayling, and brown trout being the most common ones. The European smelt is the most important baitfish for predators. Historically, the most economically significant species is the Lagsild, also known as the European Cisco. During winter, ice fishing is a popular activity, with either ice rods, or hard lines with lure.

A number of international events have been held at Lake Mjosa. In 1975 the 14th World Scout Jamboree was organized here with more than 17 000 scouts from 91 different countries. In 1995 a Swedish team lifted a Halifax Bombay from the lake’s waters, which was shot down in World War II.

Ruins of a 12th century cathedral can be visited on the east coast, north of Hamar.

Mjøsa Fish Species

Pike
European perch
Common roach
Grayling
Hunder trout
European smelt
European cisco