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l,~oag 118 . the ability to COncentrate seleniua troa the soil into . biologically available tora which could be toxie to 11 vestock. . So began tbe story ot -loco- veed- poisoning in tbe wen. I!laergillg tirst as a disease ot llvestock grazed on open range. ~~.~~ is now a major coneern for wetlands and wild- life areas in arid seetions of the West where drainage from irrigation supplies mucb of tbe water. In 1983, selenium contamination was identified at Kesterson National Wildlife Refuge (NWR) in central California. At tbis site, all fish exeept mosquitofisb (Gaabusia atflnis) disappeared, deformed waterfowl were found, and populations of birds de- clined (Marsball, 1985; Oblendorf and others, 1986). Artieles in the news media (Secramento Bee, Sept. 8-10, 1985) suggested there eould be several other wildlife areas in the West subject to tbe same type of contamina- tion. In "86".-tlle- Department of the Interior. b.qan-~econna~sance stucl1-es of .ir::.igation-drainaqe -in' nTne .areas in seven Weste::A-States. The areas we~cho;en following examination of known water quality, local geology, presence of irrigation, and proxiaity to State or national waterfowl areas. These studies were designed to deter- mine whether irrigation drainage had caused or had the potential to cause harmful effects on human health, fiSh, and wildlife, or if it might reduce the suitability of water for benefi- cial u.es. During the reeonnaissance studies, samples of water, sediment. and biota were collected twice during a two-year perlod. Results from these studiee identified areas in Califor- nia. Nevada, Wyoaing, and Utah that had problems requiring detailed study and an additional 11 sites were chosen for reconnaissanee investigation in 1987 and 1988 (fig. 1). This paper provides an overview of the potential. for selenium contaai- nation of water in the western United . '. States, .bows a general aechani.m for tbe uptake &ad mobilization'ot leleni- um in aquat ic coamun i tie., and pre.ents ezaaple. of selenium-induced problems in wildlife. Emphasis i. on wildlife areas in Utah, specifically in the aree of tbe Green River, one of tbe areas selected for detailed study by the Department of tbe Interior in 1987. SELENIUM IN THE PHYSICAL ENVIRONMENT Selelli_a ts-.wi.c!eIy ,51stribund in.cru.tal ..tertal of tbe Eartb with an abundanee of about 0.09 part per million (Lakin, 1972). It is most co..on-in-igfteOD.-.aterlaLs associated witb sulfift-a.iner1l1'S, but may be present in large concentration in certain sedimentary depos its. In prebistoric times, much of the western United States was flooded by marine and non-.arine seas. and there are now large areas where sedimentary deposits of these seas are at or near the surface. As most agriculture is on sedimentary materials, it is this source which is of the most concern in tbe enviro_t. There is a s~<J'-oorrel.1rt ion bet_ -~ ...growth..4f -seleniUII-.concen- tr.1:-~--9S98ut-i4ll-.nO- -out CT'Ops--ef Juuaa-io--alld-Crrtac-eOllS. -Yo"filitTOh s (Trelease and Beath, 1949, figs. 32, 33). Rosenfeld and Beath (.1964, tables 1-7) further identified 61 specUi~ <je01Cl9ic.'forllaUODS in south- ern .Utah ,___tbvestern-Colorado, . and Wyoai.luJ-~ ~o-be.generally- .elenif- erous .or _ se1eai-ferous' in par t. Seleniferous .formations are thoAe capable of--contributlng-alslolved foras of .selaniua to soils. Selenium then .ay be bioaccumulated by seleniUll-coDcentrating vegetation such as Astragalus. The generalized loca- tions of these deposits in the western United States are shown in figure 2. Ma., or lhe-sedi1llentary-deposi ts that cont&iA.eleDium a1ao contain large quaDtitle.-o~-.9aporTt.. wbich