Finland has a relatively high number of lakes. This is the result of the Finnish climate, which is temperate and wet, and the characteristics of the Finnish bedrock and soil.
Most Finnish lakes are shallow and contain only a little water.
Lake and river systems consist of lakes and the rivers that connect them. The waters of lake and river systems flow into the sea via a main river called an outlet.
Watersheds are flat, boggy areas located in high elevations. They divide lake and river systems from each other. The primary watersheds of Finland are Maanselkä and Suomenselkä.
Groundwater is water that is located under the Earth's surface.
Surface water is fresh water that is located above the Earth's surface.
Waste waters and the nutrients contained in them cause lake eutrophication. This is why proper waste water treatment is important.
Key words: outlet, surface water, groundwater, eutrophication, lake and river system, watershed.