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Executive Summary Stanford (1994) suggested that studies funded through the Recovery Implementation Program for Endangered Fish Species in the Upper Colorado River Basin include more of the Colorado River ecosystem than just the endangered fishes. This report describes methodology to monitor the abundance and distribution of benthic macroinvertebrates, standing stock of organic matter, periphyton chlorophyll a concentration and biomass, and water temperature. These organisms provide basic components of the food chain supporting the endangered fishes that are the primary target of the recovery program. In the event that a basin-wide monitoring program is not implemented, the guidelines presented here can be used to implement invertebrate studies as part of investigations of smaller scope. The proposed monitoring program divides the major rivers into sampling strata based on geology, large tributary stream confluences, the presence of endangered fish populations, and previous fish and invertebrate investigations. Samples should be collected from all major habitat types within each strata using appropriate sampling equipment. Initially, basin-wide sampling should be done biannually, in early spring before upper basin runoff and in fall after the summer thunderstorm season. Initial sampling could be less intensive in river reaches where some information on the invertebrate community is already available. At a minimum, insects should be identified to the genera level except Chironomidae which should be identified to subfamily. Ash-free dry weight of organic matter collected with invertebrates should be determined and chlorophyll a concentrations of periphyton samples should be measured using standard methods. The design. and implementation of this, or any other, monitoring program should be an iterative process. Sampling locations and methods can be added, removed or modified as results are evaluated or Recovery Program priorities change. 111