Abstract
Salinity is arguably the biggest water quality challenge facing the Colorado River, with estimated damages up to $750 million. The salinity of the river has doubled from pre-dam levels, mostly due to irrigation and reservoir evaporation. Natural salinity sources – saline springs, eroding salt-laden geologic formations, and runoff – still account for about half of the salt loading to the river. Consumptive water use for agricultural irrigation concentrates the naturally- occurring salts in the Colorado River water, these salts are leached from the root zone to maintain crop productivity, and the salts reenter the river as agricultural drainage water. Reservoir evaporation represents a much smaller cause of river salinity and most programs to reduce the salinity of the Colorado River have focused on agriculture; these include the lining of irrigation canals, irrigation efficiency improvements, and removing areas with poor drainage from production. Salt loading to the Colorado River has been reduced because of these efforts, but more work will be required to meet salinity reduction targets.