Densities of Corophium curvispinum Sars, 1895 collected from stones at two localities (Lobith and Nijmegen) in the Lower Rhine at a water depth of 2-3 metres during 1992 were found to be very high. At both localities Corophium was the dominant macroinvertebrate, outnumbering all other species by many times. The population of the zebra mussel (Dreissena polymorpha) was further reduced in 1992, because all stones are covered with a 1-4 cm thick layer of muddy tubes of Corophium. Muddy material including macroinvertebrates fixed by Corophium was found to be 61-609 g DW m-2 and 9-99 g AFDW m-2 stone surface.