Mjøsa is Norway's largest lake covering an area of 365 square kilometres. The name probably stems from the Norse word Mjors, meaning "glittering" or possibly Merso which means "shining".
- Length: 117 kilometres between Lillehammer and Minnesund.
- Greatest width: 15 kilometres between Hamar and Totenvika
- Altidude: 123 metres
- Greatest depth: 453 metres. Unconfirmed depths of 475 has reputedly been found.
- Average depth: 178 metres
Since 1858, Mjøsa's waterline has risen 3,61 metres dues to the construction of two dams; the Sundfoss and Svanfoss dams. The two dams were built to accomodate steamboat traffic on the
Vorma river and for
hydroelectric power.
Gudbrandsdalslågen empties in Mjøsa at its north end. The river mostly contains water from lake
Lesjaskog but also from the
Jostedalsbreen glacier.
At the south end of Mjøsa, the Vorma river starts, joining Norway's largest river Glomma at Vormsund. Glomma ends in the sea at Fredrikstad.
In addition to these two major rivers, 17 smaller ones and some 130 streams end in Mjøsa.
Three counties border on lake Mjøsa; Hedmark to the east, Oppland to the west and Akershus to the south. The three major cities along the lake's shore are Lillehammer, Gjøvik and Hamar.
Skibladner, the world's oldest paddle steamer in scheduled service, plies between the towns and villages around Mjøsa, like it has done since 1856.
Mjøsa have been flooded several times over the past two hundred years; 1789, 1860, 1895, 1910, 1927, 1937, 1939, 1967 and 1995. The 1789 flood was by far the biggest, raising the water level 9 metres above the normal, trigging a massive exodus from the surrounding areas in the following years. Today, this flood goes by the name of Stor-Ofsen.