Abstract-The Fluxes of Agrochemicals into the Marine Environment (FAME) project, which was funded by the European Union, studied the presence and fate of pesticides in major European river/estuary systems. As part of the cooperation within FAME, samples from four rivers were sent to all participants. Each laboratory analyzed the samples with a range of techniques, thus creating a database that could not have been developed through individual efforts. In the present study, compounds are identified that are important to the contamination of the marine environment on the basis of their environmental concentrations and toxicological properties. Two risk assessment methods are used. The toxic unit method, which provides a first indication of the relative contribution of compounds to the total toxicity of a sample, and the inverse method of Van Straalen and Denneman, which has been used to assess the ecological risk of a selected set of compounds (i.e., atrazine, simazine, alachlor, and metolachlor). Environmental concentrations of these target compounds were determined at different seasons during a period of at least 1 year and, hence, variations in ecological risk patterns for different European river/estuary systems could be identified. The application of the risk assessment procedures is hampered by a lack of toxicological data. It is concluded, however, that pesticides exert a significant pressure on the aquatic system. To our knowledge, this is the first joint study in which the ecological risks of modern pesticides related to different European river/estuary systems are compared.