Dedicated field trips in 2007 and 2008, focused on collecting brackish water molluscs on Tholen (Zeeland, the Netherlands), revealed two locations where the rare gastropod Heleobia stagnorum could be spotted, namely the ‘Karnemelkspot’ and the ‘Pluimpot’. Living specimens where found only at the latter locality. Ecrobia ventrosa and Potamopyrgus jenkinsi are much more common on Tholen.