Massive influxes of waste water and sludge discharges from treatment plants increased the percentage of sludge and the organic matter content in the sediment off the coast of Barcelona (Western Mediterranean Sea). A total of 22 species of cumaceans were recorded in this area at depths between 5 and 70 m. The distribution of these species was essentially depth-dependent, though at the deeper stations the distribution pattern was significantly correlated with the organic matter content. This aspect was particularly pronounced in the case of Iphinoe rhodaniensis, which attained maximum density levels of up to 573 ind. m^-2 in the vicinity of the two major sites of eutrophication. Moreover, the increased percentage of sludge facilitated colonisation of species such as Leucon affinis and Leucon siphonatus, which have been typically considered as bathyal species.