A nationally consistent framework for identifying interstate waters with applications for the national listing of fish advisories.

A 1988 survey, funded by the US Environmental Protection Agency (EPA) and conducted by the American Fisheries Society, identified the need to standardize the approaches for evaluating risks and developing fish consumption advisories that are comparable across different jurisdictions. A major tool for evaluating the progress in developing such nationally consistent information is EPA's web-based National Listing of Fish Advisories (NLFA) database, which has archived fish advisory information since 1993. The NLFA comprises both a database and Geographic Information System mapping components that are implemented using the National Hydrography Dataset (NHD). EPA and the US Geological Survey have developed an enhanced NHD product (NHDPlus) that is applied to define an interstate waters framework for the conterminous USA. This NHDPlus-based framework provides an efficient watershed-oriented approach for identifying interstate advisories from NLFA. We provide summaries of (1) the degree of consistency documented for inland waters where states have issued advisories for shared interstate NHD reaches and (2) the patterns for interstate advisories organized according to the ecoregions developed for EPA's Wadeable Streams Assessment. Approaches are also discussed for addressing interstate consistency issues for fish advisories in coastal waters making use of the NHDPlus combined with other nationally consistent frameworks, such as the 12-digit hydrologic unit code subwatersheds in the Watershed Boundary Dataset. Probability survey methods are recommended as a way to promote increased interjurisdictional consistency in the development of the monitoring and risk assessment conclusions reflected in NLFA, as well as in other EPA water quality-based programs.