Nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) were determined in different freshwater organisms from the surface waters in the Glatt Valley, Switzerland Rather high concentrations of the compounds investigated have been found to occur in macrophytic algae, particularly Cladophora glomerata (up to 38 mg kg-1, 80 mg kg -1, and 28 mg kg-1 of NP, NP1EO and NP2EO, respectively), the bioconcentration factors of NP reaching up to 10000. The concentrations in fish were much lower (NP: <0.03-1.6 mg kg-1, NP1EO: 0.06-7-0 mg kg-1, and NP2EO: <0.03-3.1 mg kg-1) indicating that biomagnification did not take place. Similar concentrations to those in the fish were determined in different tissues of a wild duck. The estimated bioconcentration factors in fish tissues ranged from 13 to 410 for NP, 3 to 300 for NP1EO and 3 to 330 for NP2EO.