This study aimed to identify the microalgae and assess their seasonal distribution in Oglat Eddaira lake (south western Algeria), integrating ecological evaluation through diatom and phytoplankton-based indices (EPI-D and Q Index). Sampling was carried out monthly from October 2023 to August 2024 using a plankton net for microalgae, with three fixed points for seasonal assessments. A total of 32 microalgal species were recorded, belonging to six classes: Bacillariophyceae, Chlorophyceae, Cryptophyceae, Conjugatophyceae, Cyanophyceae, and Euglenophyceae. Seasonal heatmaps revealed clear clustering patterns, with nutrient-related parameters (NO₃⁻, PO₄³⁻, NH₄⁺) exerting the strongest influence on microalgal assemblages, followed by physical factors (temperature, turbidity) and mineralization parameters (conductivity, salinity). The Q Index proved particularly sensitive to detecting bloom-forming species and early eutrophication signals, while the EPI-D index provided a more integrative perspective on long-term diatom community shifts. Notably, cyanobacteria exhibited higher abundances during warmer periods, indicating their role as early indicators of ecosystem imbalance. Additionally, we successfully developed a new ecological mapping of Oglat Eddaira, providing a visual representation of its environmental gradients and biological patterns, which constitutes a valuable tool for wetland management and monitoring.