Two myxosporean species: Sphaerospora renicola Dyková et Lom, 1982 and S. molnari Lom, Dyková, Pavlaskova et Grupcheva, 1983 were recorded for the first time in Poland. They were found in young carp after first overwintering in cold- and warm-water ponds. Localization of different developmental stages in carp tissues is described. Differences in frequency of particular developmental stages were noticed between the cold and warm ponds. In fish taken from cold ponds spores occurred rarely. In fish from the warm pond spores were abundant, but extrasporogonic stages were practically undetectable. Symptoms of spring sphaerosporosis are described. They were mainly connected with the presence and release of spores, and were much more serious in carp from the warm pond.