Lake Constance--a model for integrated lake restoration with international cooperation

Lake Constance is the second largest prealpine European lake. Its international catchment area lies in the territories of the four European countries Austria, Germany, Liechtenstein and Switzerland. Since the fifties, a significant degradation of its state was observed as a result of the pollutants of more than 1.2 million inhabitants in its catchment area. To counteract this negative development, international cooperation was realized in the International Commission for the Protection of Lake Constance (IGKB). Thereby the phosphorus concentration in the lake water, after a maximum value of 87 mg/m3 phosphorus in 1979, was reduced to 13 mg/m3 until 2001. To prevent the negative effects of unfavourable climatic conditions resulting in an incomplete vertical circulation, the concentration of phosphorus must be reduced to 10 mg/m3. Crucial points in future are to sustain the present successes in lake protection, to reduce existing loads as much as possible, to compensate for loads which are not avoidable and to avoid future loads. A sustainable use of the lake is ensured only by an intact lake ecosystem.