Enhanced eutrophication of lakes due to high nutrient loads from anthropogenic sources has become a worldwide problem. Dying ecosystems and limitation of uses are the consequences. In Bochum, Germany, Lake Ümminger is an integral part of a recreation area, but also receives high nutrient loads from the local sewer system, as could be shown with the help of water and nutrient balances. Mass algae growth, the dying of fish and production of digestion gas implied a demand to rehabilitate the lake. Primarily, the urgency and sanitation potential as well as the applicability of external and internal enhancement measures had to be evaluated. The trophic classification needed was based upon the German guideline for the classification of the water quality of natural lakes according to trophic criteria, mainly using Vollenweider's eutrophication model. This paper focuses on a description and analysis of the problems that arose during the application of this model to Lake Ümminger, stating that shallow, artificial lakes cannot be evaluated correctly with the existing methods. Although some suggestions for further improvement are given, the development of new evaluation criteria was not in the scope of the study presented.

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