In this paper I introduce protection measures and management options which are applied to the watershed as well as to the reservoir itself and later their impact on water quality is discussed. Emphasis is given to nutrients from non-point sources and nutrient removal from such sources by pre-reservoirs is considered in detail. Phosphorus removal has to work mainly during flood events, when most of the nutrient load enters the reservoir. As our results reveal, 55% of the total annual TP-input can be removed in pre-reservoirs. I also introduce our concept of fishery management, which involves stocking the reservoir with lake trout (Salmo trutta lacustris) and pike perch (Stizostedion lucioperca). The advantage of having lake internal management options available, i.e. selective take-off from raw waters, is also considered in the case of development of metalimnetic blue-green algal (Planktothrix) populations. Preparatory measures i.e. cleaning of the reservoir basin, which has to be done before the rivers are impounded, are discussed. “Trophic upsurge”, in the sense of nutrient leaching, was not important during the first filling years. Improvements in water quality during the “ageing process” are due to lake internal mechanisms, i.e. the increase of sedimentation capacity and decrease of the ratio of epi- to hypolimnetic water volume, which were supplemented later by sewage diversion. Our results present ample evidence that it is due to our philosophy of integrated water quality management that Große Dhünn Reservoir is oligotrophic today - always able to fulfil its purposes.

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