The "Ecoelectricity Project" headed by the EAWAG (Swiss Federal Institute for Environmental Science and Technology) aims to develop an ecolabel as an economic instrument for the promotion of ecologically sound hydropower generation. However, it is not always quite clear which methods of electricity generation can be considered unobjectionable in environmental terms. Hydropower operations, in particular, present a certain dilemma: On the one hand, hydropower is a renewable energy source without emissions and hence desirable from a global perspective. On the other hand, hydropower operations can be highly detrimental to the local and regional aquatic ecosystems. As a result, there is a need for an objective, scientifically based method for the ecological evaluation of hydropower operations. The EAWAG "Ecoelectricity Project" is developing such a method together with a process for the certification of "green hydropower".