Lake Ammersee is located 35 km north to the northern periphery of the Alps and was formed during the last glacial period ("Isar-Loisach-glacier") some 15,000-20,000 years ago. With a maximum depth of 81 m and a volume of 1.8 billion m3 Lake Ammersee is the third largest lake of Bavaria. The lake measures 15 km from north to south and reaches a maximum width of 5.5 km. The catchment area is 21.3 times as large as the lake itself. The main inflowing River Ammer (representing 72% of the catchment area) originates in the Alps ("Ammergauer Alpen"). The rates of loading are comparatively high. The water residence time is 2.7 years. Thirty-two% of the catchment area consist of woody vegetation-half is afforested plantation of conifers (Picea, Pinus) and half is mixed deciduous forest consisting mostly of beech (Fagus silvatica). Additional 56% are farmlands (69% pasture land, 31% crop field).

Surrounding settlements are mostly rural. As Munich, the capital of Bavaria with a population of 1.5 million, and Augsburg with a population of 440,000 inhabitants are situated nearby (25 km), the area is frequented for recreation activities.

The lake has been influenced by economic development since the 1950's by nutrient loading (municipal sewage). The rate of eutrophication slightly slowed down by installing a circular sewer line system in 1971 in addition to a treatment plant at the lake outlet. An improvement in the lake's trophic situation from eutrophic to now mesotrophic within the last years has taken place due to the completion of six treatment plants with chemical treatment (phosphorus removal) in the catchment area of River Ammer (built in the years 1981 and 1987) and to the regulation of total phosphorus concentration in German detergents since 1980 (Q1, Q2).