A model called SWAT was used to study water quality in the Nakdong River Basin. The researchers divided the basin into 67 parts and looked at data on rainfall, runoff, and pollutants over 6 years. They found that non-point sources contribute a lot to pollution during the wet season. Nutrient levels are higher in the dry season, especially in areas with urban sewage. The load duration curves show that sediment levels are higher in the rainy season, while nutrients like T-P are more concentrated during low flow. This method can help understand pollution in the whole watershed.