Bibliogr. s. 176-177

A phenomenon of migration of species native to the Tatra Mountains, observed in recent years, is characteristic particularly of representatives of the genus Didymosphenia (Bacillariophyceae). Didymosphenia geminata and D. tatrensis occurring in the area of the Tatra Mountains, began to distinctly dominate also in other water biotopes (including streams below the limestone Tatra Mountains). They have recently been observed also in the rivers: Białka, Dunajec and Didymosphenia geminata also in Orawa River. Their intense development has been noticed in the Białka River and Dunajec River (downstream of dam reservoirs). The colony forming species were abundantly attached to stones by means of branched stalks. This undoubtedly indicates that conditions in these environments are benefi cial to their growth. The presence of these species particularly in the Dunajec River fl owing through the Pieniny Mountains contributes markedly to the changes in phycofl ora of the river and threatens this of the Pieniny Mountains.