4.5 River Basins
to freshwaters to designate the highest and best uses (e.g., drinking water supplies, recre- ation) for conservation within the surface waters. Each classifcation has an associated set of water quality standards to protect those uses. All waters must at least meet the standards for Class C (fshable/swimmable) waters. Te other primary classifcations provide addi- tional levels of protection for water contact recreation (Class B) and drinking water (Water Supply Classes I through V). Streams, rivers, and lakes may have several classifcations applied to the same area because they protect diferent uses or special characteristics of the waterbody (NCDWR 2014c) . Water classifcation data are available from the National Hydrography Dataset (NHD), a database that interconnects and uniquely identifes the millions of stream segments or reaches that comprise the surface water drainage systems in the United States. Te NHD provides a national framework that allows information to be linked by stream reach address to an organization thereby allowing water quality data to be shared with other organizations, analyzed using a Geographic Information System (GIS), and easily integrated into many diferent types of applications to the beneft of all (EPA 2014b) . Datasets containing water classifcation information is available online from http://www. horizon-systems.com/nhdplus/NHDPlusV2_data.php. 4.5.2 Aquatic Biodiversity and Imperilment Te southeast region has the highest aquatic species diversity in the entire United States (Burr and Mayden 1992; Taylor et al. 1996; Warren et al. 2000; Williams et al. 1993) . Southeastern fshes make up two-thirds of US fauna, and nearly half of the North American fsh fauna (Burr and Mayden 1992) . Molluscan diversity in the region is globally unparalleled, with 91% of all US mussel species found in the southeast (Neves et al. 1997) . Crayfsh diversity and global importance in the region rivals that of mollusks (Taylor et al. 1996) , and crayfsh in the southeast comprise 95% of the total species found in all of North America (Butler 2002a) . North Carolina freshwa- ters support a signifcant proportion of that diversity with at least 210 freshwater fsh, 125 mollusk, and 45 crayfsh species native to the state. Unfortunately, patterns of imperilment for aquatic species are similar amongst taxonomic groups. Collen et al. (2014) reports almost one in three freshwater species is threatened with extinction worldwide which, in comparison, is proportionally greater than the risk of extinction for terrestrial species (Burkhead 2012) . More than two-thirds of the nation’s freshwa- ter mussel and crayfsh species are extinct, imperiled, or vulnerable (Williams et al. 1993; Neves et al. 1997; Master et al. 1998) . Te majority of these at-risk species are native to the southeast.
• North Carolina ranks third among southeastern states in number and percentage of imperiled fshes (Warren et al. 1997) .
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2015 NC Wildlife Action Plan
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