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. . Total salt concentration in the river system varies with the water supply. The record high flows of the early 1980's flushed and refilled reservoirs. Salinity declined at Imperial Dam from a 1982 high of about 940 mg/L to a 1986 low of about 55 mg/L, but by 1987 salinity had rebounded to 700 mg/L. Without implementing controls on salinity, the Bureau of Reclamation estimated that salinity at Imperial Dam could rise to 1,005 mg/L by about A.D. 2010. Thus, concern over high salinity have stimulated numerous studies and an elaborate control program. Under the Colorado River Basin Salinity Control Program, the Bureau of Reclamation has constructed, or proposes to construct, channel modifications that regulate salinity downstream. Water with TDS of less than 500 mg/L is considered good drinking water. Above 500 mg/L, significant municipal and industrial costs are incurred. When water contains 700-850 and more mg/L TOS, agricultural losses become significant. The solution to the problem is to keep at least 1.2 million mt of salt from entering the system annually. All seven Colorado River Basin states have joined efforts to adopt standards and implement a plan to decrease salinity while continuing to develop water supplies. For example, the Grand Valley Unit of this program consists of a series of canals and pipelines to divert saline water from entering the Colorado River downstream from Grand Junction, Colorado. Progress on the many aspects of this program are made available through the Bureau of Reclamation's Quarterly Reports on the Colorado River Water Quality Improvement Program. Other Natural Pollutants . . . . . A forest fire/flooding event recently poured debris into upper Colorado River at the Utah state line, killing off most the native and exotic fish life below the Black Rocks section Westwater Canyon. Anthropogenic Sources of Water Pollution Anthropogenic water pollution is becoming an increasingly common problem to Colorado Plateau streams. Sources of pollution typically reflect land use priorities in the region, including agriculture, grazing, mining, acid precipitation and urban sources, as well as thermal pollution. Natural geologic sources (strata containing calcium orthophosphate), and numerous anthropogenic sources have increased phosphate concentrations in Utah streams during the 1980's. Un-ionized ammonium pollution has become a problem during winter months in several tributaries in Colorado, including the Yampa, Eagle, Dolores, San Miguel, Fraser and East Rivers. Lead, copper, zinc, cadmium, and other heavy metal pollutants derived from mining activities pose a threat to the excellent water quality of high elevation tributaries, the of in . . . 26 .