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Biomanipulation (as defined by Shapiro) and top-down or consumer controlled forces refer to the control of natural aquatic organisms to improve water quality instead of through nutrient management. A cornerstone of biomanipulation studies was established during the late fifties and early sixties when the effect of fish on water quality via zooplankton predation was shown. Biomanipulation through animals other than fish or zooplankton has also been noted. The classical limnological concept of lake tropho-dynamics goes from nutrients through phytoplankton to zooplankton and fish. Therefore, top-down forces as a potential tool for manipulation was seen as a pioneering approach. During the seventies, many studies on trophic cascading effects of fish through zooplankton predation on phytoplankton have been carried out. The removal of Macrophytes by grass carp has also been investigated and was implemented as a practical way of controlling these plants. During the eighties the concept of biomanipulation was broadened to include other aspects of the complex interactions between food-web components such as the different nutrient flux pathways. In order to be able to make long term predictions for water quality improvement in lakes and reservoirs, the combined analysis of both top-down and bottom-up forces is required. (DBO)