The Freshwater Lake Water Quality Management System (FLAQUM) was developed to assess lake water quality. Results showed that during heavy rainfall, pollutant levels from nonpoint sources exceeded normal levels. In scenarios with increased pollution, BOD, T-N, and T-P concentrations were higher than agricultural water standards. Most scenarios showed mesotrophication or eutrophication, indicating excess nutrients. However, removing 60% of pollution sources led to concentrations that met agricultural water quality standards.