The ''Neue Donau'' (''New Danube'') at Vienna was erected for flood protection reasons, but turned out to be a water resort area close to the City Center (bathing, swimming, surfing along 40 km of beaches). At Vienna, a hydropower plant on River Danube (Vienna-Freudenau) is under discussion. This paper discusses various alternatives in order to keep the trophic state of New Danube as is at present, but takes also into account left bank water resources questions as well as the hygienic situation (bathing, swimming, surfing). A comparison of all alternatives indicates that, as eutrophication of New Danube is phosphorus driven, precipitation of P in wastewater treatment in the upstream drainage area is the best solution in respect to the situation of New Danube, the overall drainage basin and the receiving Black Sea. (author).