Rehabilitation and restoration measures for Elsterstausee lake (Leipzig)

The Elsterstausee is an artificial lake constructed in 1933 south of the city of Leipzig. It has an area of 50 ha, an average depth of only 2 m and between 1970 and 1991 had been intensively utilized for fish rearing. The consequent excessive nutrient loadings together with the supply of nutrient-rich water from the Elster river produced a highly polytrophic state, with Secchi depths seldom exceeding 0.4 m and a pH which often exceeded 9.0. Because of ammonia levels of 1.5 to 4.0 mg per litre, fish kills often occurred and the lake was unsuitable for bathing, for which it was originally intended. In 1991, a comprehensive programme of lake restoration was commenced, with the total removal of nutrient-laden water and the remaining fish population, consisting of carp and whitefish. The water was replaced by a supply of treated groundwater which consisted of a combination of mine drainage water and leachate from spoil heaps subjected to a natural biological treatment, including iron and manganese removal, during passage through a 1600 m long ditch. In addition, the lake was restocked with 4000 carnivorous fishes, to control whitefish populations and 5-7 kg of water fleas (Daphnia spp) were introduced annually during the recovery period. As a result of these measures the condition of the water body improved and its trophic status changed from 5 (hypertrophic) to 3 (entrophic) according to the Klapper scale. (Full translation price on application).