Abstract
Due to anthropogenic stress, the character of the Rαbień peat-bog reserve is changing, and large parts of it are being transformed into a transitional peat-bog. During more than 23 years of research, considerable changes have been noted in water pH (from 4.63 to 6.64), trophic status, and the species composition of algae. The subject of the research carried out in 2004—2005 were Bacillariophyceae and Chlorophyta. A decrease was observed in the number of species characteristic of high peat-bogs in favor of alkaliphilic species and those occurring in eutrophic waters.