The report of one specimen of the exotic species Musculium transversum in the river Eem was reason for exploring the river between Eemdijk and Eembrugge on December 9, 2006. In that part of the river littoral zones were absent due to the presence of sheetpile walls at both banks. However, some juveniles were found in a small eroded cove near the ferry bridge on the right bank at Eemdijk, and a range from juvenile to adult of M. transversum was found in a wet strip at the left bank north of Eembrugge (Fig. 1) in which its typical habitat was present, a mixture of sand and mud enriched with detritus.