Eutrophication constitutes a serious threat to many European lakes and many approaches have been used during the past 20201330 years to improve lake water quality. Results from the various lake restoration initiatives are diverse and the long-term effects are not well described. In this study, we evaluated data from more than 70 restoration projects conducted mainly in shallow, eutrophic lakes in Denmark and the Netherlands. Special focus was given to the removal of zooplanktivorous and benthivorous fish, by far the most common internal lake measure. In more than half of the biomanipulation projects, Secchi depth increased and chlorophyll-a decreased to less than 50% within the first few years. In some of the shallow lakes, total phosphorus and total nitrogen levels decreased considerably, indicating increased retention or loss by denitrification. The strongest effects seemed to be obtained 420136 years after the start of fish removal. The long-term effect of restoration initiatives can only be described for a few lakes, but data from manipulated lakes indicate a return to a turbid state within 10 years or less in most cases. One of the reasons for the lack of long-term effects may be internal phosphorus loading from a mobile pool accumulated in the sediment. Synthesis and applications. Lake restoration, and in particular fish removal in shallow eutrophic lakes, has been widely used in Denmark and the Netherlands, where it has had marked effects on lake water quality in many lakes. Long-term effects (> 8201310 years) are less obvious and a return to turbid conditions is often seen unless fish removal is repeated. Insufficient external loading reduction, internal phosphorus loading, and absence of stable submerged macrophyte communities to stabilize the clear-water state are the most probable causes for this relapse to earlier conditions. Journal of Applied Ecology (2007) 44, 1095 20131105doi: 10.1111/j.1365-2664.2007.01363.x
