This study evaluates the changes of a fresh water pond ecosystem after biomanupulation. The following experiments are included : 1. Study on silt treatment in the Oude Leie (Oeselgem). 2. Biomanipulation of the Schelde en Leie meanders and monitoring ecological cycles. 3. Monitoring ecological cycles on Spettekraai (reference site). 4. Evacuation of bream in Berlare Broek. 5. Evaluation of biomanipulation in the Oude Schelde (Kerkhove). After treatment, water quality will be measured monthly. In addition, the composition of fytoplankton, zooplankton and the fish communities will be sampled on regularly basis.