Restoration of the underwater nature in the Alde Feanen area

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Commissioned by the Province of Friesland, Witteveen+Bos is working on the ecological restoration of the aquatic environment in National Park and Natura 2000 area, the Alde Feanen in Eernewoude. The majority of the Alde Feanen park consists of turbid water with many algae and almost no submerged aquatic plants. The project includes management measures to stimulate aquatic plant growth in the Alde Feanen park and thereby significantly increase the nature value of the area.

A hydrological and ecological system analysis showed that the turbid water and lack of aquatic plants is not caused by external influences, but by an unfavourable composition of the food web in the area, where bottom-feeding and water flea-eating fish prevail. Subsequently, ten areas in the Alde Feanen with a total water surface of 80 hectares were temporarily isolated from the environment, after which the fish stock was reduced in cooperation with ATKB and local professional fishermen. Seeds, spores and remains of submerged aquatic plants from the area were also introduced to stimulate the rapid growth of aquatic plants.

The preliminary results are very positive. Following the reduction of fish stock, the water in nine out of ten areas became clear and full of plant life, and there were many positive effects on water quality and biodiversity (aquatic plants, fish stocks, birds). One area is particularly difficult to isolate and, as a result, the effect of reducing fish stocks was negated since fish from surrounding areas were still able to access it and the water is still turbid. The clear water in the nine areas is clearly visible on satellite images. In September, the results of the project were inspected with the client while snorkelling!