plies to a specific spatial area—a defined waterbody—and is expected to be met over all areas of that waterbody. Thus, identifying the waterbody of interest, whether a lake, a stream segment, or areas of an estuary, is a first step in setting water quality standards. Waterbodies vary greatly in size—for example, from a small area such as a mixing zone below a point source discharge on a river to an estuary formed by a major river discharge.
Water quality standards themselves consist of two parts: a specific desired use appropriate to the waterbody, termed a designated use, and a criterion that can be measured to establish whether the designated use is being achieved. Barriers to achieving the designated use are the presence of pollutants and hydrologic and geomorphic alterations to the waterbody or watershed.
A designated use describes the goal of the water quality standard. For example, a designated use of human contact recreation should protect humans from exposure to microbial pathogens while swimming, wading, or boating. Other uses include those designed to protect humans and wildlife from consuming harmful substances in water, fish, and shell-fish. Aquatic life uses are intended to promote the protection and propagation of fish, shellfish, and wildlife resources.
A designated use is stated in a written, qualitative form, but the description should be as specific as possible. Thus, more detail than “recreational support” or “aquatic life support” is needed. The general “fishable” and “swimmable” goals of the Clean Water Act constitute the beginning, rather than the end, of appropriate use designation. For example, a sufficiently detailed designated use might distinguish between beach use, primary water contact recreation, and secondary water contact recreation 2. Similarly, rather than stating that the waterbody needs to be “fishable,” the designated use would ideally describe whether the water
2 These uses are defined differently from state to state. In Ohio, primary contact recreation includes full body immersion activities such as swimming, canoeing, and boating. Such streams or rivers must have a depth of at least 1 meter. Secondary contact recreation includes activities such as wading, but where full body immersion is not practical because of depth limitations. The fecal bacteria criteria are less stringent for secondary contact recreation than for primary contact recreation.