Threats to the Environment
The Pasvik River has seven hydroelectric power stations that were built between 1955 and 1978. However, the one at Jäniskoski (now located in Russia) was first built at the end of the 1930s but the dam was destroyed during the war in 1944.There are three Russian hydropower stations downstream from Lake Inari: Kaitakoski, Jäniskoski and Rajakoski. The power stations at Hevoskoski, Skogfoss, Melkefoss and Boris Gleb are located along the border between Russia and Norway. Hevoskoski and Boris Gleb are Russian, and the other two Norwegian. In addition, on the Finnish side there is also a smaller hydroelectric power station on the River Kirakkajoki, which runs into Lake Inari. Due to the relatively flat terrain, the reservoirs for the power stations cover large areas of land. In order to increase the energy production of the power stations on the Pasvik River, the water level in Lake Inari is regulated by the Kaitakoski dam in the upper courses of the river. Most of the water that would otherwise have to be discharged past the turbines of the power stations are stored in Lake Inari, and are released into the Pasvik River during the low water period. In its natural state the annual variation in the water level in Lake Inari was earlier 1.25 m. Nowadays the regulated variation is 1.5 m. The most significant changes caused by the regulation of Lake Inari are the half meter (on the average) increase in the water level during the ice-free period, and the constant water level during summertime compared to the natural decrease prior to regulation. The impacts of regulation on the Pasvik River and Lake Inarijärvi The Pasvik River watercourse is one of the largest systems of rivers and lakes in the Arctic Region. Construction of the dam system has caused radical changes in its hydrological regime. Rapids and stretches of river with a strong current have disappeared and the occurrence of slow-flowing water areas has increased. This has had the most negative effect on species that prefer habitats with a strong current. Regulation has also had an effect on the aquatic macrophytes. Due to changes in the currents many of the shallows along the Pasvik River have become overgrown. The spring floods, which used to inundate extensive riverbank areas above the narrow rapids, no longer occur. Some flood meadows, where rare eastern plant species used to grow, have disappeared due to earth moving activities or the damming associated with regulation. The reduction in the spring flood also delays the ice break-up during spring. Regulation of the flow and construction of reservoirs has led to emergence of also some other specific ecological problems. For example, flooding of soil and vegetation cover and change in the hydrological regime caused changes in the organic matter flows and more intensive accumulation of organic matter into the water reservoirs. Farming in the Norwegian coastal area is another factor. All this causes eutrophication
Excess nutrient load in a water body increases primary production and causes eutrophication.Negative effects of eutrofication include decrease of water transparency, increase of algal blooms, filamentous algae and aquatic macrophytes, wintertime oxygen depletion and changes in fish community, among others.