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into six major sections. A brief description of each section is pre- sented below to enable the reader to move directly into those areas of particular interest. Section I. Abiotic Components Changes in water quantity and quality represent one of the major reasons for the population decline of many fish species. This section deals with physical and chemical aspects of the Colorado River system which directly affect the well being of its fishes. Section II. Biological Components This section represents a brief description of the biological components of the Colorado River, the role each plays in the environment, and their relationship to the important fishes. Section III. Species description This section presents a detailed discussion of the threatened and endangered fishes of the Colorado River as well as other important fishes of the system. Past and present distribution of each species and their life history are described in as much detail as the literature would allow. This section contains the most inclu- sive discussion of the fishes dealt with in the report. A dis- cussion of speciation introduces the section. Section IV. River Basin Descriptions The focus of this section is on the major sub-basins that comprise the upper Colorado River drainage basin. The history and character of each basin are described in detail as is the distribution of fishes within each. Section V. Major Factors Inducing Environmental Change This section is a general discussion of those factors that have brought about declines or alterations in the population of the endemic fishes of the upper Colorado River system. Mechanics of their effects are discussed as well as the results. Section VI. Urgent Needs and Recommended Research Priorities This section summarizes what the authors feel are the important issues which need to be answered concerning the status of Vill