New localities of Carex aquatilis in the province Friesland are reported. The species grows practically always in company of C. acuta, much more rarely together with C. vesicaria. Although C. aquatilis resembles C. acuta so closely as to cause frequent confusion, the authors through thorough acquaintance learned to distinguish both species already from some distance. Carex aquatilis differs from C. acuta in its colour, which is a somewhat glossy yellow-green, produced by the underside of the leaves, whilst the inflorescence is typically paniculate reminding one of the situation in Cladium mariscus; in C. acuta bracts and spikes are gracefully curved to one side, hence the synonymous epithet C. gracilis.