EN
During phytosociological studies conducted in old river beds of the San river within the area of the Kotlina Sandomierska basin, the occurrence of two associations of aquatic vegetation was recorded: Lemno minoris Salvinietum natantis (Slavnić 1956) Korneck 1959 and Hydrocharitetum morsus ranae van Langendonck 1935 with participation of Salvinia natans. Taking into account the fact that this is a protected species and it has been recognized as vulnerable (V) in Poland, as well as the fact that old river beds where it occurs are ecosystems which become more and more rare in our country, the described old river beds were proposed for active protection in the form of an ecological ground lot.