The Snake River near Idaho Falls, Idaho. The agricultural industry in southern Idaho is dependent on the Snake River and its tributaries for its water supply (photograph © 1978 by W.H. Mullins and published with permission).
Water quality in the upper Snake River Basin is degraded by numerous anthropogenic activities, including both nonpoint and point sources of pollutants. A 1988 assessment by the Idaho Department of Environmental Quality documented that, of 5,732 river miles assessed for nonpoint source effects in the Idaho part of the basin, 2,913 river miles were degraded by agriculture; 1,766 miles by hydrologic modification; 197 miles by construction activities; 35 miles by forest practices; 134 miles by mining; and 109 miles by other activities, primarily recreation [1]. Other nonpoint sources of pollutants in the basin include beef and dairy cattle feeding operations, atmospheric deposition, and rangeland grazing. These nonpoint sources contribute sediment, bacteria, nutrients, and pesticides to streams and can result in alterations in stream habitat and water temperature. Primary point sources in the upper Snake River Basin include industrial discharges, municipal wastewater-treatment facilities, and fish farms. Permitted discharges from these point sources during 1985-90 were about 269 billion gallons per year [2]. Primary pollutants associated with point sources include nitrogen, phosphorus, and organic wastes.
The types and geographic distribution of land use and land cover, the types and numbers of industries and municipalities using the water resources, and the manner in which the water resources are used are factors that create the water-quality conditions in the upper Snake River Basin as described in this report. Approximately 18,000 square miles of rangeland compose roughly one-half of the basin area. Forested and agricultural lands compose 23 and 21 percent, respectively, of the upper Snake River Basin. Urban areas compose less than 1 percent of the basin area. The geographic distribution of these land-use/land-cover categories has a large effect on the quality of water in the basin. Primary land uses and land cover in the mountainous northern and eastern parts of the basin are forested land and rangeland, and although forest practices and grazing may degrade water quality, water resources and the aquatic biological communities in these areas are generally of high quality. In contrast, agricultural activities, urban communities, and industries concentrated on the Snake River Plain, primarily along the Snake River and near the mouths of major tributary valleys, contribute sediment, fertilizers, organic compounds, and other pollutants to the Snake River and its tributaries [3,4]. As a consequence, stream- and ground-water quality and biological communities in the downstream parts of the upper Snake River Basin have been degraded by anthropogenic activities [4,5,6].
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About 71 percent of Idaho's crops are produced in the upper Snake River Basin. Primary crops include potatoes, beans, sugar beets, alfalfa, and grains (photograph © 1976 by W.H. Mullins and published with permission).
A large part of Idaho'seconomy relies on irrigated agriculture, which subsequently relies on adequate supplies of water. In 1990, 71 percent of all irrigated acreage in Idaho was in the upper Snake River Basin, where potatoes, beans, wheat, sugar beets, alfalfa, and barley are the predominant crops [2]. These agricultural lands are areas where pesticide and fertilizer applications and crop rotation and tillage practices degrade stream and ground-water quality. Although crop yields are improved by applications of fertilizers and pesticides, the increased production often comes at the expense of water quality.
Streamflow regulation in the upper Snake River Basin for irrigation and hydroelectric power production has a detrimental effect on the water chemistry and biology of streams. During the irrigation season (April to October), much of the water in streams is diverted to canals for irrigation needs. These diversions reduce streamflows, to the detriment of the biological communities [6,7]. Fifteen large hydroelectric power facilities, generating about 1.2 million megawatthours of electricity annually, and numerous smaller facilities provide a large percentage of Idaho's electrical output [2]. Although hydroelectric power facilities generally do not produce pollutants, the dams, diversions, and canals associated with the facilities commonly change streamflow characteristics and alter habitat conditions for various species of aquatic organisms [7].
Since 1980, the number of beef and dairy cattle in the basin has grown substantially [8]. Beef and dairy cattle operations (confined-animal feeding operations) discharge some pollutants directly to streams; however, their wastes have a larger effect on ground-water quality [9]. In many areas where the cattle industry is growing, nitrate concentrations in ground water are already high because of fertilizer applications and manure production. Pollutants reaching ground water in the upper Snake River Basin eventually return to the Snake River, providing additional nitrogen and phosphorus to many streams where eutrophication problems are already evident [3,4].
Although urban areas compose less than 1 percent of the basin area, they are a potential source of pollutants to streams and ground water. Major urban areas in the basin are Idaho Falls, Pocatello, Rexburg, and Twin Falls, which together account for about 30 percent of the total basin population. These four cities discharge nearly 7.5 billion gallons of treated wastewater annually to the Snake River and its tributaries [2]. Areas in the Wyoming part of the basin do not have a large resident population but do have a significant influx of people each summer because of tourism and recreational opportunities. In 1990, nearly 3 million people visited the Grand Teton and Yellowstone National Parks. In some parts of the basin, the population is expected to grow substantially in the future. Projections indicate that by 2010, the population in the basin will reach 480,000, a 20-percent increase from the 1980 population [2]. An increasing population will put increasing pressure on the quantity and quality of the water resources in the basin. Urban runoff has the potential to transport fertilizers, organic compounds, and trace elements from streets, parking lots, and lawns to streams and ground water. Fish-tissue and bed-sediment samples collected downstream from urban areas during the National Water-Quality Assessment (NAWQA) study contained some of the largest concentrations of organic compounds in the basin [10].
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Recreation in the upper Snake River Basin has become increasingly popular, primarily in Wyoming and in the Henrys Fork Basin. Yellowstone and Grand Teton National Parks in Wyoming attract nearly 3 million visitors a year (photograph by M.G. Rupert, U.S. Geological Survey).
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Numerous dams, like this one on Jackson Lake in Grand Teton National Park, provide storage for downstream water needs. Many of the dams in the upper Snake River Basin also are used to generate hydroelectric power (photograph © 1995 by W.H. Mullins and published with permission).
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The growth in the number of confined-animal feeding operations has become a concern in parts of the basin. Animal wastes can pollute streams and ground-water supplies (photograph © 1995 by W.H. Mullins and published with permission).
Although point sources of pollutants account for only about 2 and 1 percent of the total nitrogen and phosphorus, respectively, introduced annually to the upper Snake River Basin [3], they typically discharge directly to streams where pollutants become immediately available for uptake. Primary point sources of pollutants in the basin are industrial discharges, municipal wastewater-treatment facilities, and fish farms. Three industrial facilities, 13 wastewater-treatment facilities, and 12 fish farms are permitted to release 269 billion gallons of effluent in the upper Snake River Basin annually [2]. In addition, numerous other smaller, unpermitted point sources of pollutants exist in the basin. Of the total discharge from point sources, about 95 percent is from fish farms; most of the water passing through the fish farms is supplied by springs downstream from Milner Dam. Wastewater-treatment facilities account for only about 4 percent of the total point source discharge in the basin [2]. However, wastewater-treatment effluent is typically more enriched in nitrogen, phosphorus, and organic wastes than is the effluent from fish farms and, in some areas of the basin, accounts for a disproportionate amount of the pollutants entering streams [4].
