The WASP6 model was used to predict water quality in a lake, helping managers choose the right water quality policies. Tourists were found to be the main source of pollution, contributing significantly to nitrogen and phosphorus levels. The model predicts that BOD, T-N, and T-P levels will increase in the future, requiring action to reduce pollution. The Suokjeong reservoir currently has good environmental grades, but water contamination is expected to worsen over time. Urgent measures are needed to control nutrient levels and prevent eutrophication.