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'. C.") ~:) .... 00 w programs developed and carried out by the Federal Government but also measures instituted by and implemented by the states and local entiti~s. The river's salinity problems were also recently featured in the October 1973 issue of National Geographic article entitled "The Bittersweet Waters of the LO\~er Colorado". SALINITY PROBLEMS OF THE COLORADO RIVER The basic causes for the Colorado River's high salinity are both natural and man made. The primary natural causes are the saline shales underlying much of the Upper Colorado River Basin. Even though precipitation falling on the high peaks of the Rocky Mountains runs off in mountain streams with a low salinity, by the time these streams have joined to form the major rivers draining the basin and have picked up runoff and seepage from the underlying shale formations, the Colorado River is carrying a heavy load of dissolved salt. It is estimated that the sal~ load at Lee Ferry, the dividing point between the Upper and Lower Basins, was approximately 5 million tons a year under natural conditions. Man's activities have added to this problem, as the consumptive use of water in irrigation and other activities remove water from the system but return all of the dissolved salts back to the river, concentrating the salts in a smaller volume of water. Also, when irrigators apply water to their crops on lands that overlie the saline shales, the excess applied 'later is flushed through the soi 1 and underlying shales, thus sending additional salts back to the river. Salinity also increases as a result of reservoir evaporation, transbasin exports of low salinity water, and municipal and industrial uses. It is estimated that currently the river carries approximately 8.5 million tons of salt each year at Lee Ferry in a flow less than that under natural conditions. Diversions arp, mana fol': th~ l,as Ve-gAS Are-A at l..akp. Mead.. Hithout any salinity 2 ,i;