The distribution and ecology of Sphaerium solidum, S. rivicola, S. corneum, and S. lacustre in the estuarine area of the Rhine, Meuse, and Scheldt are described. Attention is drawn to the fact that in these estuaries no lamellibranchs occur in water with salinities of between 1‰ and 5-10‰ Cl’, which is in accordance with the well-known brackish water curve of Remane (1940).