Section 303(d) of the federal Clean Water Act (CWA) and the U.S. Environmental Protection Agency's (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. For each WQLS, 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 that water quality standards are being met. The Lower Gunpowder Falls (basin code 02-13-08-02), located in Baltimore County, MD, was identified on the States list of WQLSs as impaired by heavy metals (1996 listing), nutrients (1996 listing) and evidence of biological impacts (2002 listing). All impairments are listed for the non-tidal streams. This report provides an analysis of recent monitoring data, including hardness data, which shows that the aquatic life criteria for heavy metals and the designated uses supported by those criteria are being met in the Lower Gunpowder Falls. The term heavy metals and metals are interchangeable and generally interpreted to include those metallic elements from periodic table groups IIA through VIA. At trace levels, many of these elements are necessary to support life. However, at elevated levels they become toxic, may build up in biological systems, and become a significant detriment to aquatic life.