Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental Protection Agencys (EPA) implementing regulations direct each state to identify and list waters, known as water quality limited segments (WQLSs), in which current required controls of a specified substance are inadequate to achieve water quality standards. This list of impaired waters is commonly referred to as the 303(d) list. For each WQLS, the State is to either establish a Total Maximum Daily Load (TMDL) for the specified substance that the waterbody can receive without violating water quality standards, or demonstrate that water quality standards are being met. Middle Patuxent River (basin code 02131106), located in Howard County, Maryland, was identified on the States list of WQLSs as impaired by zinc (Zn) (1996), sediments (1996), nutrients (1996), and impacts to biological communities (2004 listing). The information used for listing Zn is suspect due in part to sampling and analysis methods available at the time, and assessment inconsistencies that led to the listing in 1996.