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<br />'1 <br /> I <br />I <br />! <br />., e-' <br /> I c, <br />., <br /> <'.J <br /> I~;'" <br />., '.- ~. <br /> I ,., <br /> ~-, <br />.. I <br />I <br /> <br />:.1 <br /> <br />" <br /> <br />"'.' <br /> <br />: ~ <br /> <br />.} <br /> <br />.;,; <br /> <br />,.: <br /> <br />~: . <br /> <br />INTRODUCTION <br /> <br />After the discovery of contaminated irrigation return waters in the San loaquin Valley of <br /> <br />central California in the early 1980s (Ohlendorf et aL 1986, Saiki 1986), the Department of the <br /> <br />Interior (DOl) initiated the National Irrigation Water Quality Program (NIWQP) in 1985 to <br /> <br />identify other irrigation drainages in the western United States with similar water quality <br /> <br />problems (Feltz and Engberg 1994, Engberg 1998). These illVestigations focused on DOl <br /> <br />irrigation projects where the receiving water was a national wildlife refuge or had the potential to <br /> <br />impact migratory birds or endangered species. The San luan River, located in northwestern New <br /> <br />Mexico and southeastern Utah, was identified as one area needing further study. <br /> <br />Five DOl irrigation projects on the San Juan River return water by overland flow, <br /> <br />seepage, or subsurface tile drains to the main stem or to the ground-water system in the San luan <br /> <br />River basin. Extensive irrigation outside DOl projects influences water quality in the tributaries <br /> <br />and main stem of the San Juan River (Blanchard et aL 1993). It is estimated that irrigation return <br /> <br />flows, after completion of the Navajo Indian Irrigation Project, may comprise about 15% of the <br /> <br />annual flow of the San luan River (USGS et aL 1989), <br /> <br />The San Juan River provides critical habitats for two federally-listed endangered fish <br /> <br />species, Colorado pikeminnow (Ptychochei/us lucius, formally named Colorado squawfish) and <br /> <br />razorback sucker (Xyrauchen texanus; USFWS 1994), and two species of concern, flannelmouth <br /> <br />sucker (Catostomus latipinnis) and roundtail chub (Gila robusta; USFWS 1996). A small <br /> <br />. , reproducing population of Colorado pikeminnow exists in the San luan River in the area from its <br /> <br />~.. . <br /> <br />confluence with the Animas River near Farmington, NM, downstream to Lake Powell (USFWS <br /> <br />1990). <br /> <br />Radiotelemetry studies of Colorado pikeminnow in the San luan River suggest that <br /> <br />1 <br />