level). Another nearby mountain is Halleberg. Environment Environmental monitoring studies are conducted annually. In a 2002 report, the data showed no marked decrease in overall water quality, but a slight decrease in visibility due to an increase of algae. An increasing level of nitrogen had been problematic during the 1970s through 1990s, but is now being regulated and is at a steady level. Some bays also have problems with eutrophication and have become overgrown with algae and plant plankton. Fish Vänern 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, pollution and the M74 syndrome. Sport fishing in Vänern 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. In the open waters of Vänern, the most common fish is the smelt (Osmerus eperlanus), dominating in the eastern Dalbosjön, where the average is 2,600 smelt per hectare. The second most common is the vendace (Coregonus albula), also most prominently in Dalbosjön, with 200–300 fish per hectare. The populations may vary greatly between years, depending on temperature, water level and quality. Salmon Lake Vänern has two remaining sub-groups of land-locked Atlantic salmon (Salmo salar), locally known as Vänern salmon ("Vänerlax"). They are both native to Lake Vänern and the parental fish all must spawn in the adjacent running waters to ensure survival and produce offspring. The first sub-group is named after an eastern tributary to the lake, Gullspångsälven, and is therefore called the Gullspång salmon ("Gullspångslax"). The second strain is the Klarälv salmon ("Klarälvslax"), mainly spawning in the Klarälven River drainage system, which is over 500 km long. The Klarälv salmon historically migrated as far as 400 km upstream into Norway to spawn in the northerly sections of the river. These two sub-groups of salmonids are more related to the Baltic stocks than to North Sea stocks (Palm et al., 2012), and have both in their isolation distinctively developed in Lake Vänern for over 9,000 years (Willén, 2001). They are also very notable in that they have never entered the ocean and instead followed the deglaciation of Sweden's inland watersheds at the end of the Last Glacial Period. In the 1800s, annual catches in both Vänern and Klarälven were high