With a length of 19.5 km and a maximum width of 3.3 km Attersee is the largest lake within the Austrian borders. According to its glacial origin, most of the western and northern part of the lake is characterized by moraine material. The eastern and southern area consists of flysch and limestone respectively. Situated in the prealpine region of Upper Austria, the lake and its immediate area is primarily used for agriculture and touristic recreation. Attersee is the last link in a chain of lakes within the catchment area. Fifty-five percent of the surface inflow of the lake comes from Mondsee, via a 2 km-long river. This tributary contributes up to 60% of the total annual phosphorus load to Attersee. However, the lake is still to be classified as oligotrophic. The construction of a system of sewers collecting domestic sewage was finished in 1980. This measure was taken in order to prevent eutrophication due to continuously increasing tourist activities.