Algal communities are sensitive to environmental changes and serve as effective bioindicators for assessing water quality in aquatic ecosystems. This study analyses the seasonal presence of algal species in a freshwater system to determine their correlation with pollution levels. Using data from the provided dataset, Pearson correlation coefficients were calculated to explore relationships between algal species presence across the rainy, winter and summer seasons and their potential as pollution indicators. Seasonal variations in phytoplankton diversity highlight the significant influence of environmental factors-including temperature, light and nutrient availability-on phytoplankton dynamics in Rajaram reservoir, offering critical insights for ecological monitoring and water quality management. The consistently high Palmer’s Algal Pollution Index (PAPI) scores, exceeding 20 across all three seasons, confirm persistent organic pollution in Rajaram lake throughout the year. Nygaard’s Compound Index further verifies eutrophic to hypereutrophic conditions, with the most extreme nutrient enrichment observed in summer, where pollution-tolerant species with high AGPI scores (e.g., Microcystis aeruginosa and Euglena gracilis) dominate, reflecting intensified organic pollution driven by elevated nutrient inputs from agricultural runoff. The overall algal community composition confirms that summer conditions exacerbate water quality deterioration through increased runoff and favourable growth conditions for pollution-tolerant and bloom-forming species. These findings reinforce the sensitivity of algal assemblages as effective bioindicators, highlighting the need for targeted seasonal monitoring and management strategies to mitigate eutrophication and organic pollution in the studied aquatic system.
