Lake Vanern is the largest lake in which country?

Lake Vanern is the largest lake in Sweden, the largest lake in the European Union and the third-largest lake entirely in Europe after Ladoga and Onega in Russia. Geologically, the lake was formed about 10,000 years ago; when a glacier melted, the entire width of Sweden was covered in water, creating a strait between Kattegat and the Gulf of Bothnia. Due to the ensuing post-glacial rebound, lakes such as Vänern and Vättern became closed off. As a result, there are still species remaining from the ice age not normally encountered in freshwater lakes. A Viking ship was found on the lake's bottom on May 6, 2009.

Lake Vanern covers an area of 5,655 km2 (2,183 sq mi). Its surface is 44 m (144 ft) above sea level and it is on average 27 m (89 ft) deep. The maximum depth of the lake is 106 m (348 ft).

Vanern has many different fish species. Locals and government officials try to enforce fishing preservation projects, due to threats to the fish habitat. These threats include water cultivation in the tributaries and pollution.Sport fishing in Vanern is free and unregulated, both from the shore and from boats (with some restrictions, e.g. a maximum of three salmon or trout per person per day). Commercial fishing requires permission. An increasing level of nitrogen had been problematic during the 1970's through 1990's, but is now being regulated and is at a steady level.