Ecological Assessments of Seven Lakes in Antalya River Basin: Application of Phytoplankton Indices and Multimetric Approach

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ABSTRACT Human‐induced pressures and global climate change are increasingly degrading freshwater resources worldwide. Continuous monitoring of these systems is therefore essential for assessing their ecological health. In this study, species–stressor relationships and ecological status were evaluated across seven lakes in the Antalya River Basin using phytoplankton‐based indices and multimetric approaches. Canonical correspondence analysis identified key environmental drivers of phytoplankton distribution, including electrical conductivity (EC), total organic carbon (TOC), total suspended solids (TSS), pH, and dissolved oxygen (DO). These variables together explained 94.5% of the variation in species–environment relationships. Among the studied lakes, Lake Kırkgöz exhibited the highest water temperature (19.8°C) and EC (574 μS cm −1 ), whereas Lake Eğri had the lowest temperature (14.7°C) and Lake Küllü the lowest EC (73 μS cm −1 ). Elevated TOC concentrations were mainly observed in high‐altitude lakes, particularly Lake Küllü, while moderate‐altitude lakes such as Eğirdir and Gölcük showed higher DO levels. Phytoplankton community composition varied significantly among lakes, resulting in different trophic states. Based on total phosphorus, total nitrogen, Secchi depth, and chlorophyll‐a, Lake Eğri was classified as oligotrophic, Lake Eğirdir as mesotrophic, and the remaining lakes as eutrophic. The Modified Phytoplankton Trophic Index (MPTI) showed a strong relationship with log‐transformed total phosphorus (R 2 = 0.89), indicating good ecological status for Lake İlvat, poor status for Lake Kırkgöz, and moderate status for the remaining lakes. Multimetric biological (BCG) and chemical (ABOZ) assessments supported these patterns, identifying Lake Kırkgöz as the most degraded system and Lake İlvat as having the highest ecological status. Overall, this study highlights the importance of integrated multimetric approaches that combine biological and physicochemical indicators for robust assessment of lakes' ecological status.