Final TMDLs Approved by EPA: St. Mary's Lake

St. Mary’s Lake is an impoundment located near Leonardtown in St. Mary’s County, Maryland.  The impoundment, which is owned by the Maryland Department of Natural Resources, lies on Western Branch a tributary of St. Mary’s River.  An earthen dam was constructed in 1975 for the purposes of flood control, recreation and fish and wildlife. 

St. Mary’s Lake was identified on the State of Maryland’s 2002 draft list of Water Quality Limited Segments [303(d) list] as impaired by mercury contamination, based on data for mercury concentrations in fish tissue.  Concentrations in the water are well below the threshold for concern in regard to drinking water.  The Maryland water quality standards Surface Water Use Designation [Code of Maryland Regulations (COMAR] for St. Mary’s Lake is Use I – Water Contact Recreation and Protection of Aquatic Life.  The Maryland Department of the Environment’s (MDE) current public fish consumption advisory to eat limited amounts of fish from St. Mary’s Lake is not supportive of this use.  Therefore, the document available below establishes a Total Maximum Daily Load (TMDL) for mercury in St. Mary’s Lake. 

TMDL of Mercury for St. Mary's Lake, St. Mary's County, Maryland

(Approved on February 23, 2004)

EPA's Decision Letter

EPA's Decision Letter

Main Report


Comment Response Document



Contact Information

Please direct questions or comments concerning this project to Maryland's TMDL Program at (410) 537-3818.