For efficient water quality management of Saemangeum lake, it is very important to accurately analyze discharged load characteristics using investigated pollution sources data from Saemangeum watershed. Investigation of pollution sources was conducted from 2003 to 2007. In this study, pollution sources are largely classified into human population, livestock, industry, and land use. Discharged loads of BOD, T-N and T-P from classified pollution sources were calculated by Korea TMDL (Total Maximum Daily Load) technical guideline. The calculated results showed that the major sources of BOD and T-N were land use, human population, livestock, and industry in order. However, the major sources of T-P were livestock, land use, human population, and industry in order. Our results clearly show that pollution sources of the priority management for water quality enhancement in the Saemangeum lake has represented land use and livestock.