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Objectives 4 and 5. Physical and chemical sampling has been completed for 154 sample sites and most of the data from these investigations have been entered into a database. Where field collection records were not available, data was obtained from the New Mexico Surface Water Quality Bureau STORET database for New Mexico and incorporated into our master database. Twenty-five chemical, physical and climate variables were used to delineate general boundaries for aquatic ecoregions in New Mexico. The purpose of this is to facilitate the study of fish and benthic macroinvertebrate distributions within regions where the composition of the biotic communities might be expected to be similar. Four aquatic ecoregions have been identified that intersect major drainage boundaries and physiographic provinces. This indicates an underlying similarity among sites that is more related to elevation and growing season length rather than to physiography, surface or subsurface geology. Aquatic Ecoregion 1 includes sites above about 2135 m (7000 ft) in at least five major drainage basins in the state. Within Aquatic Ecoregion 1, there are two subgroups of sites which differ mauily'in substrate composition; one group, generally at higher elevation, has a higher percentage of boulder substrate and lower percentages of gravel and sand than does the other group. Aquatic Ecoregion 2 includes sites from about 1675 m (5500 ft) elevation up to about 2135 m. These sites differ from the higher elevation sites of Aquatic Ecoregion 1 by having a significantly higher percentage of silt substrate, higher substrate embeddedness, longer growing season length, and greater watershed area. Aquatic Ecoregion 3 represents sites from about the. 180 frost free isoline, located variously between about 1340 m and 1370 m (about 4400 ft and 4500 ft) elevation up to about 1675 m. Aquatic Ecoregion 4 includes sites with a growing season length greater than 180 frost free days. In New Mexico, this is restricted to the downstream ends of the Rio Grande, Pecos, Canadian, Mimbres, Tularosa, and Gila drainages. The multivariate analyses used to define the aquatic ecoregions were also useful for identifying "outlier" sites, i.e., sites that were very different from other sites near them. A manuscript of these findings is appended to this report (Appendix 3). The co- authors of this report intend to publish these findings in a peer reviewed scientific journal. Objective 6. The effects of environmental stressors on fishes have traditionally been assessed in New Mexico at low levels of biological organization. Retrospective assessments of stress on aquatic communities have had two foci. First, stress assessment has been oriented toward the health of individual fish and it has focused on measuring physiological functions of individual fish, rates of deformities or disease, condition, incidence of parasitism, and tolerance to specific contaminants. The second perspective for assessment of stress in fish has been focused on site- specific trends in the abundance, growth rate, and distribution of populations. At the community level, assessment has involved simple comparisons of taxonomic richness or indices of diversity estimated for different points in time. Our efforts are directed toward extending site-specific assessment to a regional framework. To accomplish this, we need to understand how benthic macroinvertebrate, chironomid and fish faunal assemblages are structured by underlying physical, chemical, and climatic features of their environment prior to large-scale impacts by humans. The report in Appendix 2 (and to a lesser degree, the report in Appendix 1) (n