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from natural sources while 37 percent result from irrigation.22 Salinity affects the quality of the drinking water that comes from the Colorado River in the Lower Basin and also makes the water less .desirable for other domestic, municipal. and industrial uses. It can limit the types of crops that can be grown as well as the yield of those crops. In 1961, when highly saline drainage water from the Wellton-Mohawk Division of the Gila Project in Arizona pushed salinity levels in the Colorado River at the Mexican border to more than 2,000 parts per million of total dissolved solids, damllge to crops in the MexicaIi Valley caused an international incident. 23 One response to this incident was the passage of the Colorado River Basin Salinity Control Act in 1974.24 This law provided federal funding to construct projects in the basin that would reduce salt loading to the Colorado River. One of these projects became the Grand Valley Salinity Control Unit. The original plan called for actions that were expected to reduce salt loading to the river by as much as 410,000 tons annually. Stage I of the Grand Valley Salinity Control Unit was essentially completed in 1983. The effort focused on a 6.7 mile section of the Government Highline Canal in the western part of the Grand Valley. The canal was lined, and diversion structures for laterals were rebuilt. In addition, 34 miles of open dirt laterals were transfonned into about 30 miles of plastic pipe. In Stage II, 38 miles of the canal in the eastern part of the valley are being lined with polyvinyl chloride; 144 miles of open ditch laterals are to be replaced by pipes, The salinity control project brought pennanent change to irrigated agriculture in the Grand Valley. Because that change is still underway, it is difficult to assess its full implications. One immediate effect was that irrigation activities in the valley, practices that had been in existence with virtually no change for 50 to 70 years or more came under intense scrutiny. A system, or more accurately a collection of systems, that had met their clear objective when they were designed and constructed of providing a reliable and low cost 22 Taylor O. Miller, Gary D. Weatherford, John E. Thorson, The SallY Colorado (The Conservation Foundation 1986) at S. 23 Id. at 24. 24 Publ L. No. 93-320, 43 U.S.C.~ IS'!. I I