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1. INTRODUCTION Selenium toxicity is the presumed cause of population declines in many fish and avian species in the western United States. In particular, avian deformities at the Kesterson National Wildlife Refuge in California resulted in an emphasis on selenium toxicity in irrigated regions of the intermountain West (Presser 1994; Seiler 1998). Populations of many fish species also collapsed at Kesterson, and based on a well-documented case at Belew's Lake in North Carolina (Lemly 1985), it was assumed that selenium was responsible. Recent data published in the veterinary literature, however, indicates that historical research with selenium and livestock cannot be duplicated, and that the reported effects, in some circumstances, can be attributed to other causes. The veterinary research questions the use of tissue plugs and total selenium analyses as a means of identifying selenium poisoning in any species. This research further suggests that some presumably affected species may be adapted to high levels of selenium. Accordingly, the purpose of this project was to reinterpret the available literature in the context of data available from local fish recovery programs in the Upper Colorado Basin (Fig. 1). Assessing the decline and the attempted recovery of endangered fish in the Upper Colorado Basin is a complex undertaking because it is an interdisciplinary scientific problem in a multi- jurisdictional political environment. The latter refers not only to local and.national politicians but also to the various government agencies involved, including the Fish and Wildlife Service (FWS), the Geological Survey (GS), the Bureau of Reclamation (BOR), and various state agencies. There is little doubt that there were more and bigger fish with a wider distribution before human activities impacted the Upper Colorado Basin. There is also no disagreement regarding the fact that endangered fish in the Upper Colorado Basin have been harmed by both pollution and habitat modification. Within these broad categories, however, are several interrelated subcategories. Addressing these specific subcategories is where the problems arise. For example, no one disputes the fact that nonnative fish species prey on native fish (see Sect. 4.2). In addition, no one disputes that the populations of some of the nonnative fish are enhanced both by their ability to thrive in poor-quality water and their adaptation to the current river regime (see Sect. 4.2). Conflicts arise, however, on where to place emphasis on the endangered species recovery. Should the nonnative fish be poisoned? Should more funds go to removing selenium and other chemicals from agricultural drainage? Should emphasis be placed on returning the river to a flow regime that more closely mimics that under which the endangered fish evolved? These scientific questions are further complicated by political realities. Each of the three possibilities just mentioned has some political baggage. Poisoning nonnative fish is opposed by those who consider the native species to be "trash" fish or who utilize the nonnatives as sport fish. Cleaning up agricultural drainage is popular to those pursuing population increases and further land development because it creates jobs by bringing in federal dollars for lining ditches and canals. Blaming either selenium or nonnatives is favored by those pursuing further water development because it diverts emphasis from being placed on restoring the flow and physical characteristics of the rivers. The controversies extend to the natural resource agencies themselves. All agree that there is value in habitat reclamation, but there is considerable difference of opinion within and among the agencies regarding where and how recovery emphasis should be placed.