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.

In this study, we record diversity and ecology of aquatic Oomycetes in the Aue Lake and the river Fulda in Kassel (Hesse, Germany). We monthly collected water samples of both water bodies from July 2003 to June 2004. The baiting method was used to gain an insight into the occurrence of aquatic Oomycetes. A total of 14 species of aquatic Oomycetes belonging to the orders Saprolegniales, Leptomitales and Olpidiopsidales could be isolated of both water bodies. Numerous saprophytic isolates of Rhizophydium Schenk (Chytridiomycetes), Rhizophydium carpophilum (Zopf) Fischer, parasitic on Oomycetes, and additionally one species of Plasmodiophoromycetes, Woronina polycystis Cornu could be isolated. Many isolates of Saprolegniales attributable to the genera Achlya Nees, Dictyuchus Leitgeb, Saprolegnia Nees and Pythium Pringsheim (Pythiales), which could only be identified on generic level, could be isolated as well. The species were examined and discussed with respect to their occurrence in the stagnant water Aue Lake and/or in the running water of the river Fulda. Half of the isolated species only occurred in one of the water bodies. In this study the occurrence of Achlya proliferoides Coker could be documented for Germany for the first time. The trophic status of the Aue Lake and of the classification of water quality of the river Fulda were determined by limnological-chemical parameters obtained by simultaneous investigations of both water bodies.