We compared the seasonal occurrence of Leptomitus lacteus (Roth) C. Agardh (Oomycetes, Leptomitales) in freshwater samples from autumn 2003 to summer 2004. For this purpose, we analysed 42 different water samples of running waters from Hesse and Thuringia and additionally of stagnant waters and of a spring from Hesse. For isolating L. lacteus, the baiting technique was used. The simultaneous limnochemical characterisation of the examined waters resulted in information on the trophic status of the lakes and the water quality classification of some rivers. L. lacteus occurred in all three types of waters examined. Based on the number of samples in which it occurred, L. lacteus seems to prefer rivers rather than stagnant waters. L. lacteus could be isolated during the whole year. Nevertheless, most isolates were obtained in winter. Hence, a preference for growth and propagation in winter is postulated.