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 listed on the Integrated Report of Surface Water Quality in Maryland (Integrated Report), the State is to either establish a Total Maximum Daily Load (TMDL) of the specified substance that the waterbody can receive without violating water quality standards, or demonstrate via a Water Quality Analysis (WQA) that water quality standards are being met (CFR 2010). In 2002, the State began listing biological impairments on the Integrated Report. Maryland Department of the Environment (MDE) has developed a biological assessment methodology to support the determination of proper category placement for 8-digit watershed listings. The Potomac River Lower North Branch (LNB) watershed (basin code 02141001), located in Allegany County, was identified on the 2008 Integrated Report under Category 5 as impaired by nutrients and sediment (1996 listings), methyl mercury, and impacts to biological communities (2002 listings) (MDE 2008a). The 2008 Integrated Report specified that the designated use impaired by nutrients is Protection of Aquatic Life. The 1996 suspended sediment listing was refined in the 2008 Integrated Report to a listing for total suspended solids. Similarly, the 1996 nutrients listing was refined in the 2008 Integrated Report, and phosphorus was identified as the specific impairing substance. Consequently, for the purpose of this report the terms nutrients and phosphorus will be used interchangeably. The 2008 Integrated Report also restricted the impairment for biological impacts to 1st through 4th order streams in the watershed. EPA approved water quality assessments (WQA) for low pH and cadmium (1996 listings) establishing that water quality criteria are being met (listed in Category 2 of the 2008 Integrated Report). The listings for sediments and impacts to biological communities will be addressed separately at a future date.