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drainage specificity. The primary aspect of concordance between fish faunal regions and aquatic ecoregions in the upper Rio Grande drainage appeared to be elevation. The partial concordance between fish faunal regions and ecoregions in the upper Rio Grande drainage has been observed in other states. Hughes et al. (1994) summarized results • for --studies - in.. Missouri, -Kansas, - Nebraska, Oregon, and Arkansas. In Missouri, fish faunal regions (Pilieger, 1971; Pflieger et al., 1981) had considerable correspondence to the ecoregions of Omernik (1987). In contrast, Hawkes et al. (1986) distinguished 6 major fish regions delineated mostly by drainage that bore no resemblance to the six ecoregions of Omernik (1987). Five fish faunal regions were found to be more appropriate than the seven ecoregions of Omernik (1987) for streams in Nebraska (Bazata, 1991), although most of the fish faunal region boundaries followed closely the 7 ecoregion boundaries. In Oregon, Hughes et al., (1987) found that statewide, ecoregions offered the single most suitable system to classify fish assemblages, but alone they were insufficient. Matthews and Robison (1988) described a large river fauna in Arkansas that ecoregion and basin classifications missed. The examples above underscore potential inadequacies with Omernik's ecoregions and with river basins. Fish data offer more detailed information about fish presence/absence than ecoregions and they should be considered when developing regional expectations for fish assemblages (Hughes et al., 1994). Hughes et al. (1994) suggest that intermediate regions at the scale of drainage units or ecoregion subregions offer greater precision than basins or ecoregions at far less expense than habitat classification, but their usefulness is untested. Our results indicate that aquatic ecoregions have greater potential utility than Hydrologic Units in the upper Rio Grande drainage. When our analyses are expanded -to -a -statewide- wale; --they should determine if Aquatic Fmregions and/or Hydrologic Units offer better stratification of sample sites. Taxonomic Associations Chironomids Presence/absence data for chironomids indicate that widespread species may prove useful in identifying chironomid species that are indicative of degradation in the upper Rio Grande drainage. The high degree of specificity of chironomid species associations to individual streams and reaches within streams could prove useful in fine-scale water resources management, i.e., temporal monitoring of individual sites and tracking presence/absence of unique or rare species. Three genera of Orthocladiinae are most important in terms of chironomid species diversity, i.e., Orthocladius, Cricotopus and Eukiefferiella. Species of all three genera are scraper-gatherers that feed in the aufwuchs (periphyton) film on solid substrata; many occur as components of the madncolous7 assemblage. Moderate anthropogenie organic enrichment would be Madricolous organisms live in thin films of water on rubble, gravel, bedrock, plant surfaces or at the margins of streams or in splash zones of riffle or cascades. 23