Diatom communities of lake/stream networks in the Tatra Mountains, Poland, and the Swiss AlpsDiatom communities in alpine-zone streams of the Tatra National Park and the Swiss National Park were heterogeneous with respect to species richness, abundance, Shannon diversity index, and ecological preference. Two groups of diatoms were distinguished. Group 1, inhabited streams in the upper Gąsienicowa Valley (Tatra Mts) and Macun Lakes region (Alps), and had high species richness and Shannon diversities (especially in the Tatra Mts streams) but low abundances. The most abundant and common diatoms were