To investigate how habitat type influences species diversity and distribution of algae, 115 sampling sites across eight different habitats (stream, spring, lake, pool, wetland, ditch, trough, hot-spring) were randomly sampled from Agri province, Turkey. A total of 392 algal taxa (gamma diversity) were identified, of which 212 taxa (54.08%) belonged to Bacillariophyta while the rest (180 taxa) belonged to seven other groups (Chlorophyta, Charophyta, Euglenophyta, Cyanobacteria, Miozoa, Ochrophyta, and Cryptophyta). 150 taxa were encountered only once. The highest alpha diversity was found in ditches (H' =4.57, 235 taxa) followed by streams (H' = 4.40, 238 taxa), and the lowest diversity was recovered in troughs (H' = 2.62, 42 taxa). Relatively high Whittaker's beta diversity (Bw = 19) indicated a low level of similarity among sampling sites suggesting that no common taxonomic group was solely effective enough to change dominancy level of any species among the habitats. The first two axes of Canonical Correspondence Analysis accounted for 58.1 % of the total variance in the occurrence of 152 algal taxa (all taxa recovered from more than three samples) and described gradients across four environmental variables (habitat type, pH, elevation and water temperature). Ditches significantly contribution to alpha and gamma diversity in the province although they have relatively small surface area and shallow water compared to other habitat types. High alpha diversity in ditches may be related to the positive effect of geographic and climatic factors in mountainous area. Future possibilities are discussed. (C) 2021 European Regional Centre for Ecohydrology of the Polish Academy of Sciences. Published by Elsevier B.V. All rights reserved.