<![CDATA[The Andalas River is located in Seluma Regency, Bengkulu Province and is used by the community as a source of raw water for PDAM, however, river rock mining activities, waste disposal by rubber factories, and water extraction have the potential to reduce the water quality of the Andalas River. This research aims to analyze the diversity and abundance of phytoplankton as a bioindicator of water quality in the Andalas River. Sampling was carried out in March-April 2026 at three stations using a purposive sampling method using a plankton net, then analyzed using the Shannon-Wiener index (H'), uniformity (E), and dominance (C). The research results found 51 types of phytoplankton from 8 divisions, namely Bacillariophyta, Chlorophyta, Euglenophyta, Charophyta, Cyanophyta, Dinophyta, Ochrophyta, and Cryptophyta, with the most dominant division being Bacillariophyta. The highest diversity and abundance was found at Station 1 (32 species; 286 individuals/L; H' = 3.323), followed by Station 2 (28 species; 137 individuals/L; H' = 2.986), and Station 3 (23 species; 105 individuals/L; H' = 0.177). The dominance index values for the three stations are close to 0, indicating that there are no species that dominate excessively. Water quality varies from good condition (Station 1), moderately polluted (Station 2), to heavily polluted (Station 3). Physico-chemical parameters in the form of pH, temperature and DO show that river conditions are still within the range that supports phytoplankton life.]]>
