Environmental quality criteria are established and used in most industrialized countries to determine whether organisms, public health or materials are jeopardized by hazardous substances. The criteria are determined by means of different methods, however, depending on the legal context and individual national characteristics. This paper compares and analyses different methods used to derive quality criteria for hazardous substances in the aquatic environment. It describes various protected assets, i.e. aquatic communities, wildlife, fishery, suspended matter/sediments and drinking water supply. Special attention is focussed on a comparison of different methodologies to derive quality criteria for the protection of aquatic communities. Special emphasis is placed on compensation factors and statistical extrapolation methods that serve to assess safe environmental concentrations.