Spring ecosystems in arid regions are oftentimes the only permanent water source in the uplands and provide essential habitat for a myriad of aquatic and terrestrial organisms (Erman 2002); they are essentially aquatic islands in a sea of desert (Thompson et al 2002) . Riparian areas adjacent to springs can provide habitat to up to 75% of the available species diversity in arid regions (Shepard 1993). Spring ecosystems have evolved within a narrow set of environmental conditions strictly dependent on groundwater discharge (Shepard 19 93). Discharge of springs within Bighorn Canyon National Recreation Area (BICA) has been found to be dependent on snowmelt-based groundwater reaching outflows as recently as weeks after melting, to as long as years after (D. Schmitz, pers. comm.). The mosaic of microhabitats in springs is largely due to stable, long-term flow rates (Perla & Stevens 2003), and perennial discharg e has been linked to diverse, unique and often endemic flora and fauna (Myers 1995, Sada and Vinyard 2002). Aquatic macroinvertebrates can make up a substantial proportion of spring biodiversity. Aquatic species in spring ecosystems can display a high degree of endemism, often evolving to subtle cues in water chemistry (Arsufi 1993, Heino et al. 2003; Sada et al . 2005). Macroinvertebrate populations in springs of the Great Basin, Sierra Nevada, and Colorado Plat eau are known to support endemic aquatic macroinvertebrates (Erman 2002; Hershler and Sa da 2002; Sada and Herbst 2001). An initial survey of Great Basin Springs reported four new species of aquatic invertebrates (Myers 1995). A new species of the springsnail, Pyrgalopsis (the only species reported east of the continental divide) has recently been found in a Missouri River (Montana) spring (Hershler and Gustafson 2002). Even though most spring locations in BICA have been documented on USGS topographic maps, there has been no documentation of aquatic fauna occurring within these ecosystems. Spring flora and fauna in BICA have only been investigated for occurrence of rare riparian and wetland plants (ex.Sullivantia hapemanii var. hapemanii) (Heidel and Fertig 2000). Therefore, a survey of spring fauna will substantially increase the known BICA species and document potentially rare, endemic or endangered species. Surveys in this area will fill data gaps, serve as a reference point for change detection, provide a baseline necessary for evaluating the rarity of different spring ecosystem types, and form an understanding o biological diversity and integrity at the local and ecoregional level. Many spring species have narrow environmental ranges (specialists) and therefore are susceptible to changes in water chemistry and habitat quality Our main objectives for this study include 1) an initial aquatic invertebrate faunal survey and bioassessment of targeted perennial BICA springs, 2) determining the environmental factors that determine biointegprovide a sampling scheme and identify indicator measures (species richness, abundance, target species (i.e. endemics, etc.) with which to monitor spring diversity and biointegrity in the future. Achieving our objectives, especially the third, will allow park managers to monitor the status and changes of aquatic macroinvertebrate indicators over time within BICA springs. This process can be repeated every five years for any proposed spring-type monitoring protocol: an impaired (cattle or human impacted) sample and a reference (pristine) condition sample from each spring type