The increasing pollution with mud silt and nutrients of Duemmer Lake [West Germany] caused the destruction of the water bottom vegetation subsequently causing the loss of important nutritional, spawning and nesting sites for fish and birds. Cleaning up of the lake in several phases is proposed. The Hunte River which traverses this lake carries waste material and sediment; this material should be reduced by using suction mud barges in the western and southern portions of the lake, dumping the sediment by building a new embankment. Bypassing of the upper and old Hunte River branches by constructing a meandering canal is recommemded. The reeds should be cut in sectors and replacement biotopes should be introduced. Native organisms should be reintroduced. A population of muskrats has been present since 1964. The reed vegetation (mostly Phragmites australis) has extended only in the northeastern and eastern portions. Bullrushes (Scirpus lacustris) suffered from the increasing use of artificial fertilizers on the surrounding agricultural countryside, which caused eutrophication of the lake. Characteristic plants at various locations around the lake are described, including Nuphar luteum, carex stricta and C. gracilis, Glyceria maxima, Typha latifolia and P. australis. Roe deer, foxes, marsh harriers, reed warblers, bitterns, bearded tits and black terns are or were found around this lake.