The objective of this study is to investigate the biodiversity of phytoplankton and to identify the algal species as bio-indicators for water quality in Tajan River of Mazandaran Province (North of Iran).
A total of about 600 samples were collected from 9 stations; from Solayman Tange Dam to Caspian Sea during the period 2011- 2017. 305 species under 86 genera and 23 subspecies (totally 328 taxa) were identified under five algal divisions. The highest number of species was belonging to the Bacillariophyta including 71 species, and the lowest was for Streptophyta including 56 species. Also, the percentages of species in different algal divisions were about 21, 20, 22, 20, and 17% for Cyanoprokaryota, Euglenophyta, Bacillariophyta, Chlorophyta, and Streptophyta, respectively. Results showed that order Euglenales had the highest biodiversity (59 species). The Oscillatoriaceae was a dominant family with 3 genera and 35 species, while Oscillatoria was a dominant genus including 22 species. Referring to the stations, the highest number of Cyanoprokaryota was recorded at stations 1 & 2 (48 species), station 7 for Euglenophyta (44 species), station 5 for Bacillariophyta (41 species) and Chlorophyta (52 species), and finally station 2 for Streptophyta with 26 species. With respect to the importance of the Tajan River in north of Iran for drinking and agriculture activities, the results of this study is very important as one of the main criteria for assessing and monitoring of water quality and environment in this region with emphasis on algae interference.