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• INTRODUCTION This report documents completion of the Instream Flow Group (IFG) phase of the Colorado River Fisheries Project (CRFP) as directed by an Amendment to a Memorandum of Understanding (MOU) agreed upon by U.S. Bureau of Reclamation (Reclamation) and U.S. Fish and Wildlife Service (FWS) in January of 1981. As outlined in the original MOU, the overall objective of the CRFP was to gather and interpret data for use in resolving Endangered Species Act (Section 7) consultations regarding several proposed Reclamation projects or operations. The CRFP became a multiple project study with diverse objectives generally outlined in the executive summary. The IFG phase of the study was contracted to compliment the biologic phases by providing certain analytic tools to aid in.determining past, present, and future habitat conditions. To provide these general capabilities, IFG, in 1980, began a project component with the following objectives: 1. To gather physical habitat data at selected locations on the Green and Colorado Rivers; 2. To gather and compile temperature and other water quality related data for use in a system based water temperature model, and 3. To provide the capabilities of a physical habitat and water quality simulation system as a partial analytic framework which might aid FWS and others in resolving current endan- gered species problems. This completion report primarily describes the tools and capabili- ties available as of November 1981. Additional refinements in the model components and a more comprehensive representation of the basin's physi- cal habitat distribution are to be expected in the future. THE SIMULATION MODELS - GENERAL PHABSIM Two forms of habitat simulation were used during this period of the project. First, the PHABSIM model, developed by the IFG, was applied to six reaches, three each on the Green and Colorado River mainstems. This technique was applied as a component of the Instream Flow Incremental Methodology (IFIM) which is a systematic approach to solution of water allocation problems for stream resources. Proper use of the IFIM re- quires consideration of the watershed, food base, water quality and flow regime components of a river system, noting probable changes in each and determining the effects of such changes. Given reasonable assurance that changes in these components will be minimal or predictable, the effects