Section 303(d) of the Federal Clean Water Act requires states to identify waterbodies that are not meeting water quality standards and to develop total maximum daily loads (TMDLs) for those waterbodies. A TMDL is the amount of a pollutant that a waterbody can assimilate without exceeding the established water quality standards for that pollutant. Through a TMDL, pollutant loads can be allocated to point sources and nonpoint sources discharging to the waterbody. The study area for this project is the Spring Lake watershed in Yell County in west central Arkansas. The study area is part of the Arkansas Department of Environmental Quality (ADEQ) Planning Segment 3G and is located within the Arkansas River Valley ecoregion in Hydrologic Unit 11110204. The study area is located in the Ozark National Forest, and land use in the study area is almost entirely forest. Spring Lake was included on both the draft and final versions of the 2004 Arkansas 303(d) list as not supporting all designated uses due to a fish consumption advisory for mercury on largemouth bass. The Mercury Action Level in Arkansas for fish consumption advisories is 1 mg/kg of mercury in fish tissue. A mercury concentration of 1.05 mg/kg was measured in largemouth bass from Spring Lake. There have been no known violations of the numeric criterion for mercury in the water in Spring Lake. The estimated existing mercury load to Spring Lake included atmospheric deposition from local emission sources, regional atmospheric deposition, mercury previously deposited in the watershed and transported to the lake via erosion, and mercury in soils from geologic sources transported to the lake via erosion (background). There are no point sources discharging to Spring Lake. The largest source of mercury to Spring Lake was erosion. The existing mercury load to Spring Lake was estimated to be 0.91 g/day.