The Alde Feanen (2500 ha) is a relatively large nature reserve in the lower middle part of the province of Friesland, The Netherlands. The area consists of grass- and woodland, peat-diggings, and broads and open basin water. The nature-function -with specific ecological goals- is the main target for the water management. However, the water quality in the various waters did not agree with the formulated standards for this area. In the period 1990–1993 many restoration measures have been realised, namely isolation from the basin water, dredging, biomanipulation, and hydrological re-arrangement. A monitoring program, started at the end of 1987, follows the effects of the various measures. First results are an improvement of the water quality of hydrological isolation, and of dredging. Biomanipulation gives varying results, depending on the effectivity of the removal of bream. Local factors, such as a colony of cormorants, can nullify restoration measures. In general, water quality is improving, which gives a perspective on the re-introduction of the otter.

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