SUMMARYInvasive and alien cyanobacteria are considered as a serious threat to aquatic ecosystems due to their ability to produce cyanotoxins and outcompeting native species. Among cyanobacteria, Nostocales is a group with strong competitive advantages including the production of resting cells, ability to fix nitrogen or high affinity to phosphorus. A species Chrysosporum bergii has broadened its original distribution from brackish and seawater habitats of Caspian and Aral Seas to northern regions of Europe. The aim of our study was to expand the knowledge on the distribution of C. bergii, its preferred habitats in the invaded areas and examine whether the biomass of C. bergii is related with biomass of other alien or native cyanobacteria. We examined the phytoplankton community composition and the abiotic factors in randomly selected lakes of western Poland. For the first time, we showed that it occurs widely in lakes of this region. However, it occurred in one third of the investigated lakes and its contribution to total phytoplankton biomass was low. It occurred more frequently in shallow lakes with low conductivity and dissolved phosphorus, yet with higher total phosphorus concentration. The most remarkable finding was a negative relationship of C. bergii biomass with the biomass of native A. gracile, but a positive relationship with an invasive cyanobacterium C. raciborskii. This result suggests that these alien species occur under similar environmental conditions in Polish lakes. Moreover, the morphological features of C. bergii in Poland were similar to those of Anabaena bergii var. limnetica Couté et Preisig from Lithuania and Anabaena bergii from Czech Republic.