Of all the challenges facing the Colorado River, there’s at least one that all stakeholders are working on collaboratively, not competitively — salinity. 

Since 1974, the seven Colorado River basin states — Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming — have coordinated efforts to implement salinity control in the waterway as part of the Colorado River Basin Salinity Control Forum. The forum was created by the U.S. Congress, flowing funding through the Bureau of Reclamation to reduce the salt load in the river and research the issue. 

“The fact that the seven states, despite all of the scratching and kicking that’s going on on the water quantity side, still meet twice a year, collegially with the bureau, and everybody works together. It’s quite remarkable and sort of an anomaly,” said David Robbins, a water and environmental attorney who has been involved with the salinity control program and forum on behalf of Colorado since 1975. 

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Dave Kanzer, director of science and interstate matters for the Colorado River District, said this cooperation is related to the program’s multiple benefits. 

“We’re reducing environmental impacts. We’re increasing agricultural production and local economic growth,” Kanzer said. “It does a lot of good things.” 

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Over the past 50 years, the salinity control program has implemented systems and projects to reduce the river’s salt load by over 1.3 million tons. 

While salinity is naturally occurring, there are a few reasons that states and river stakeholders have long kept an eye on it. 

“There are scientific reasons, ecosystem reasons and then financial reasons,” said Connor Newman, research hydrologist and groundwater specialist for the U.S. Geological Survey Colorado Water Science Center. 

A baseline amount of salinity is OK. Too much salinity can have adverse effects on drinking water, water infrastructure and treatment, appliance wear, aquatic life, the productivity of certain agricultural crops (including wine grapes, peaches and other salt-sensitive products) and more. 

The U.S. Bureau of Reclamation estimates that salinity causes between $500 and $750 million annually in damages and could exceed $1.5 billion per year if future increases are not controlled. 

Understanding salinity in the Colorado River 

Simply defined, salinity is how salty water is, measured by the amount of dissolved ions and chemicals in the water. 

While most people might associate salinity with sodium and chloride — the components of table salt — in streams and the natural world, it refers to a lot of other compounds, said Bill Hoblitzell, a watershed scientist who helps to run the Eagle River Coalition’s water quality monitoring and assessment program.

“It’s also calcium, magnesium, potassium, sulfate, bicarbonate — all these other compounds that dissolve into the water contribute to salinity,” Hoblitzell said. 

The Colorado River in its entirety transports approximately 9 million tons of dissolved salt each year, according to a 2009 U.S. Geological Survey report on salinization in the Upper Colorado River.

In the river and its tributaries, salinity is both naturally occurring and exacerbated by human activity. 

“The bulk of the salt in the system is just there naturally,” Robbins said. 

Much of the Upper Basin geology — specifically Mancus and Mesa Verde shale formations — was created when it was covered by an inland sea, Robbins added. Therefore, they contain salt deposits that through natural erosion and runoff, make their way to the rivers and downstream. 

In Colorado, natural salinity sources include the geothermal hot springs in Glenwood Springs; shale cliffs and evaporating salt deposits in the Eagle and Roaring Fork valleys; and the salt domes in Paradox Valley in Montrose County along the Dolores River. 

Human activity can also exacerbate challenges by accelerating the release of compounds from these natural geologic materials and increasing the salt load in the river and tributaries, according to the 2009 U.S. Geological Survey report. This includes activities like mining, farming, petroleum exploration and urban development. 

For example, with some agricultural irrigation practices, by adding more water to the soil that naturally contains salts, “increases the rate of dissolution above the natural signal,” Kanzer said. 

The use of road salts — solid and liquid — to clear snow and ice can also lead to increased salt loads as the salt dissolves and makes its way into snowmelt and streams. 

“We do see this kind of increasing trend over time that seems to be not coming from just a natural or a background source — it seems to be coming from these human-derived sources,” Hoblitzell said. 

The source of salinity depends on where you are in the Colorado River Basin and when you’re looking.

Up-basin in Colorado River tributaries in Eagle County — where naturally occurring salinity is very low — Interstate 70 probably accounts for the largest input of salt, Kanzer said. 

Hoblitzell added that concentrations of salinity tied to roadway operations rise and peak in the spring as snowmelt begins. 

Moving downstream toward Dotsero and merging with the Colorado River through Glenwood Canyon, human sources are overshadowed by natural geologic sources.  

Downstream in the Grand Valley in Mesa County and west into Utah, agriculture and human activities start to have a larger proportional impact, Kanzer said. 

The 2009 U.S. Geological Survey report indicated that half of the salt in the upper Colorado River comes from Mancos Shale formations throughout the basin and Eagle Valley Evaporite, a rock comprised mostly of gypsum and anhydrite present throughout the northwest region of Colorado. 

As the river flows downstream, salinity increases and the problem intensifies for water users, particularly agricultural producers. 

“I like to say that second to quantity is quality of the Colorado River water. We often take for granted that if we just have the water it will be of good enough quality for our needs,” said Michael Gooseff, a faculty fellow at the University of Colorado Boulder’s Institute of Arctic and Alpine Research. “But, that’s not necessarily the case for water users, especially farmers, in the lower basin.”

What researchers are still learning about Colorado River salinity 

While there is a fairly good understanding of how much salinity is entering the basin and river each year, the understanding of where it enters is still fairly broad, according to Newman.

This is because salinity is predominantly measured by U.S. Geological Survey gauges at fixed points that can be geographically dispersed. 

Since 2018, Newman, Gooseff and collaborators have been rafting the Colorado River to better understand exactly where water quality changes — including salinity — along the river. 

“We are ultimately trying to figure out how a parcel of water is evolving as it moves downstream,” Gooseff said. 

On these floats, their boat is fixed with multiple sensors that collect data continuously, including one testing the salinity. In 2024, it also included a way to detect the presence of noble gases, like helium, which can be an indicator that there’s old groundwater discharge in the river. 

“Old groundwater is one of the most common sources of salinity,” Newman said. “Where we see the salinity go up, if the helium is also going up, that old groundwater is the source of that salinity. If we see the salinity go up, but the helium doesn’t go up, then it’s a different source. If we understand the sources, then we could potentially mitigate them to reduce the need for downstream water treatment.”

Once they’ve determined the primary inflow zones, Newman noted that the next steps will be to go back and test these sites to monitor for other factors like seasonality.   

The river’s salinity is dynamic as a result of not only broader climate change but also the changes in precipitation from year to year. 

“The climate warming, and drying signals that we’re seeing exacerbate salinity concentrations. In other words, (if) you have less water, you’re going to have higher concentrations,” Kanzer said. “We can’t underestimate the power of nature to change how we are trying to control salinity in the watersheds.”

Kanzer gave the example of a high-precipitation year. The vast majority of the Colorado River basin’s water supply comes from snowpack and spring runoff. So, in a wet year, the amount of water can increase erosion rates and bring more salt into the river — even with more dilution in the waterway.

“This give and take, and this dynamic sort of loop of factors, are all really tough to control,” Kanzer said.

Colorado River Salinity Control program 

Historically, projects funded by the Colorado River Salinity Control program have been prioritized by “dollars per ton” or the greatest amount of salt for the least amount of money, Robbins said. 

“At one point in time, we were well under $100 a ton investment. As we have picked the low-hanging fruit, that number has inched up,” Robbins said. “Basically, all that means is you’re getting less salt out for the amount of money you’re putting in.”

Overall, the goal of the program is to “balance all the different activities and operations throughout seven states and two basins to maximize the environmental benefits and agricultural productivity and quality of life,” Kanzer said.  

These projects tackle both natural and human-caused sources. A long-term project in the Paradox Valley is one significant example of the former. 

“The salinity control program, in conjunction with the Bureau of Reclamation, has devised a system where they capture a large portion of the saline groundwater (before it reaches the river), which would otherwise flow to the river,” Kanzer said of the Paradox project. “They treat it a little bit, and then they inject it into a single deep well, almost 4 miles into the earth.”

The project captures and sequesters — in the deep well — around 100,000 tons of salt that would otherwise flow downriver, Kanzer said. 

However, because natural sources are harder to control, the bulk of the salinity control is angled toward human activities, including agriculture.

“The bulk of the salt control efforts in Colorado have involved the effort to reduce unneeded irrigation water flowing into the groundwater system, dissolving salt, and returning to the river,” Robbins said. 

In most instances, this includes putting in pipelines — or other impermeable barriers — to prevent this from occurring. 

The work in the agriculture industry deals more with “controlling salinity closer to the source rather than the point of use, like the municipal (water) providers,” Kanzer said. 

The U.S. Natural Resource Conservation Service, which is part of the federal Department of Agriculture, also works directly with private landowners to convert irrigation systems in a manner that reduces “the amount of deep percolation, which is the way in which the salt is mobilized and returned to the river,” Robbins said. 

There are consequences to some of these projects. For example, installing pipelines can have environmental consequences to riparian vegetation and habitat. So, a component of the program’s investment goes toward mitigating these, Kanzer said.

A portion of the funding also goes each year to research institutions to grow the information about this perennial problem. 

While the program has made good progress over the course of the past 50 years, these improvements and enhancements are likely to continue well into the future. 

“It is sort of a chronic potential issue that’s out there because there’s so much salt in the landscape,” Kanzer said. “The investments are durable investments and have long-lasting benefits, but like anything, they wear out … and there are some areas that are still untreated.” 

In December, the U.S. Congress passed a law to increase the federal share of funds going to the Colorado River Salinity Control Program to ensure the program can continue to operate. 

“It’s an ongoing battle,” Kanzer said. “Although we’ve made progress, it’s not going away.”