The biological parameters discussed are the phytoplankton community structure, the zooplankton species composition and biomass, the abundance of macrophytes and the fish community structure in Lake Klein Vogelenzang. The biological parameters are also discussed in the RIVM-reports which discribe the development of the waterquality parameters after P-reduction measures were take in Elfhoeven and Nieuwenbroek (703711002) and biomanipulation and P-fixation studies were carried out in Klein Vogelenzang/Groot Vogelenzang (703711003). A summary report about these studies is also available (703711004).