This study evaluated the environmental impact of As and heavy metals occurring upstream of the Andong dam. In sediments, the concentrations of heavy metals were found to be higher in the dry season than in the wet season, with the highest concentration occurring near the smelter. Moreover, As concentrations in some tributaries, such as Songjeongricheon, Golpocheon, and Gacheon, were higher than those in the Nakdong River. The concentrations of heavy metals in water samples did not exceed the Korean environmental standards. However, some tributaries showed relatively high As concentrations in the dry season. In suspended sediments, As and heavy metals were detected in the wet season, and particulate transport was identified as their major dispersion mechanism. In conclusion, the abandoned metal mines, smelter, and deposited-tailings were the source of the pollutants, which accumulated on the river bed in the dry season and were carried into the Andong dam in the wet season, via streams.