The Colorado River is a vital water source for the Western United States and Mexico, originating in the Rocky Mountains and stretching 1,400 miles to the Gulf of California. Its basin spans seven U.S. states—Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming—and parts of Mexico. It provides drinking water to nearly 40 million people and irrigates 5.5 million acres of farmland, accounting for 15% of American agriculture and 90% of the nation’s winter vegetables. The river also supports diverse ecosystems, industry, and recreation. Understanding its water quality is essential.
Assessing Water Purity
Assessing the Colorado River’s purity involves monitoring indicators and substances. Key parameters include:
Salinity
Dissolved oxygen levels
pH
Water temperature
Specific conductance, which measures water’s ability to conduct electricity, indicates dissolved inorganic solids like chloride, sulfate, sodium, calcium, and magnesium. Nutrient levels, such as nitrates and phosphorus, are also tracked, along with sediment loads and metals. Water quality assessments also include emerging contaminants. These encompass:
Microplastics
Pharmaceuticals
Personal care products
Perchlorate
Selenium
Mercury
Other heavy metals
Salinity is a primary water quality concern throughout the basin. While headwaters have concentrations below 50 milligrams per liter, these can increase to about 900 milligrams per liter by the time the river reaches the international boundary with Mexico.
Sources of Impairment
The Colorado River’s water quality challenges stem from natural processes and human activities. About 62% of the river’s salt load originates naturally from mineral dissolution in geological formations like the Mancos Shale and Eagle Valley Evaporite, saline groundwater, geothermal hot springs, and salt domes. Human activities worsen these natural conditions. Agricultural runoff introduces pesticides, fertilizers, and sediment. Irrigation practices accelerate the release of naturally occurring salts from soils, increasing the salt load. Urban and industrial wastewater discharges also impact water quality, with past issues including elevated nitrate levels from septic tanks. Legacy mining operations contribute heavy metals and acid mine drainage. Dams and reservoirs, while providing water storage, alter natural sediment transport and affect water temperature and flow, influencing water chemistry and ecological conditions.
Consequences for Ecosystems and People
Impaired water quality in the Colorado River affects its ecosystems and human populations. Elevated salinity levels cause economic damages estimated between $300 million and $750 million annually in the U.S. across agricultural, municipal, and industrial sectors. For agriculture, high salinity reduces crop yields, limits crop types, and can render land unsuitable for cultivation. For human populations, compromised water quality affects drinking water supplies. High salinity can corrode lead pipes, potentially increasing lead levels. Elevated nitrate levels in groundwater, often linked to septic systems, also pose health concerns. These issues necessitate additional water treatment, increasing costs for municipalities. Aquatic ecosystems also suffer. Alterations in water temperature and flow due to dams, combined with pollutants, harm native fish and other aquatic organisms. Low dissolved oxygen, often from nutrient pollution and organic decomposition, is detrimental to aquatic life. Heavy metals and emerging contaminants can accumulate in the food chain, affecting biodiversity and riparian habitats.
Stewardship and Restoration Efforts
Efforts are underway to monitor, protect, and improve the Colorado River’s water quality. Monitoring programs, such as the U.S. Geological Survey’s (USGS) National Stream Quality Accounting Network (NASQAN) and the volunteer-based Colorado River Watch, collect data on chemical constituents, sediment, and other water quality parameters. These programs provide information for understanding trends and informing management decisions. Government agencies, including:
The Environmental Protection Agency (EPA)
The U.S. Bureau of Reclamation
State and local water authorities
play a role in regulatory oversight and improvement projects. Tribal nations also manage water quality within their territories. Non-profit organizations like:
Protect Our Rivers
Colorado Water Trust
The Nature Conservancy
Living Rivers
contribute through hands-on restoration, education, and advocacy. Efforts to enhance water quality include upgrading wastewater treatment systems for nutrient removal, sometimes incorporating artificial wetlands. In agriculture, best management practices like improving irrigation efficiency and converting to less water-intensive crops reduce runoff and salt loading. Watershed restoration projects, often using nature-based solutions like beaver dam analogs and floodplain reconnection, aim to heal degraded streams, store water, and improve ecological health. Collaborative interstate agreements, such as the Colorado River Basin Salinity Control Program, bring together states and federal agencies to address salinity.