In May 2001 the author investigated some waters near the seadike in the north of the province of Groningen, the Netherlands. The focus was on the presence of brackish water molluscs. At three localities (figure 1) live specimens of Mytilopsis leucophaeata were found. The animals were found attached to the underside of big stones lining the banks of canals and a harbour within one single watersystem near the town of Delfzijl. No other molluscs were found.