Water quality research in the Loosdrecht lakes: proposals for the follow-up restoration measures

Reduction of the external phosphorus load in 1984 did not lead to recovery of Loosdrecht lakes. Therefore the Provincial Water Authorities of the Province of Utrecht proposed, after consulting the research group Water Quality Research Loosdrecht lakes (WQL), measures to reduce the present external phosphorus loading from 0.35 to 0.1 g Pm^–2y^–1. Mathematical modelling suggested that such a reduction would benefit the water quality of the lakes. The results of the WQL investigation did not lead to additional measures (dredging, biomanipulation, chemomanipulation).