The abundant appearance of the floating Salvinia Salvinia natans (L.) ALL.on the Regalica River in Szczecin in 2016

In first decade of September 2016 an abundant occurrence of floating fern Salvinia natans was observed on waters of Regalica – one of two main river channels in the mouth part of Odra river in Szczecin, NW Poland. The concentration of 20–50 individuals per 1 meter was observed along the distance ca 2.5 km of river banks. Salvinia natas is relatively rare species in Poland, but it was previously noted as constant, but rare species in the flora of lower Odra river valley. Such massive and annual only apearrance of this species is, however, highly unusual phenomenon, and the species itself was never previously observed in this particular part of valley.