A century-old practice allows people to use more than their legal share of Colorado River water. Researchers say it should stop.

For a few weeks each spring, Kathleen Curry, a rancher and former state lawmaker, gets to use more than her legal share of Colorado's water. The extra water is vital for ranchers in her area, she said.

"Everybody puts on as much water as they can because they know, after the runoff is over, there won't be enough," said Curry, who raises cattle and hay in Gunnison County.

But new research suggests taking that extra water away to help stabilize the overstressed Colorado River Basin.

When there's an abundance of water, people can use more than their legal share thanks to a quirk of water law called the free river condition. The researchers, primarily from the University of Virginia, call the practice an archaic "loophole" that should be closed to properly manage the state's water resources.

Colorado state officials are adamantly opposed to the idea, saying the free river condition is justified by the state constitution. Farmers and ranchers, like Curry, say closing the "loophole" threatens agricultural economies. But the prospect of shrinking water supplies in the Colorado River Basin could override ranchers and the state and bring an end to the free river condition in Colorado.

"Me, the social scientist, I feel like if water is scarce ... you want a water rights system that's closed. You don't want a loophole in it," said Peter Debaere, an economist at the University of Virginia who contributed to a recent study on the free river condition.

The free river condition happens when there's more than enough water to meet all of the demands on a river. It's most common during spring runoff in May and June, when snowmelt swells Colorado's rivers and streams.

For example, people might have the right to divert 50 cubic feet per second of water from a stream. When there is more than 50 cfs in the stream, it triggers the free river condition.

That's when people with water rights can use more than their legal allocation because there is excess water available. People without water rights can also use water when the condition is in effect.

Once the flows shrink below the total allocation, it ends. This is when a farmer might call a water official to place a "call" on the river, saying they're not getting their legal allocation and requiring upstream users to cut back or stop using water.

What does free river water use look like?

The researchers stumbled on the free river condition when they were studying water scarcity in the Colorado River Basin, Debaere said.

They looked at a decade of water data for one region of Colorado, known to water wonks as Division 5. The region follows the Colorado River from its headwaters near Grand Lake down to where it crosses the Colorado-Utah border near Grand Junction.

The researchers did not calculate the excess water use under free river conditions in the three other divisions on the Western Slope, which are part of the Colorado River Basin.

In 2017, people diverted about 87,600 acre-feet more than the legal allocations in Division 5, according to the study published in Water Resources Research . Of that, about 21,400 acre-feet was used and lost for good. The rest eventually ran back into rivers and streams.

One acre-foot roughly equals the annual water use of two to three households.

The 21,400 acre-feet that typically disappears from Division 5 could instead flow downstream to Lake Powell, one of the main storage reservoirs for the Colorado River, the researchers said. Powell's storage is at a third of its capacity after recently hitting historic lows.

Or, Colorado could stop the free river condition as a good faith effort in the ongoing negotiations over the future management of the Colorado River, the researchers said. It would show the six other basin states that Colorado is doing its part to help balance water use in the basin.

Ending the free river condition might also be a less impactful way of saving water than other methods, like paying farmers not to plant crops, the researchers said.

In 2023, the System Conservation Pilot Program, an interstate water conservation effort, paid Colorado farmers nearly $1 million to save 2,517 acre-feet of water. Almost all of these projects involved fallowing land. And that water wasn't necessarily conserved: When it ran past one participant's farm, it stayed in the river and could be used by anyone downstream — including during free river conditions.

Ending the free river condition won't solve Colorado River problems, but it could help, Debaere said.

"This is a public debate. I'm not the one going to tell everybody what everybody has to do," Debaere said. "I can give my opinion, but ultimately, this is something for the people of Colorado and the people within the basin to decide."

It's not an option, state engineer says

State Engineer Jason Ullmann disagrees with just about everything in the research — the numbers, analysis and assumption that Colorado should send more water downriver.

First and foremost: The Colorado Constitution says "the right to divert the unappropriated waters of any natural stream to beneficial uses shall never be denied." That preserves a water user's right to use extra, or unappropriated, water when a river is flowing high, Ullmann said.

He said the researchers' numbers are too high based on the state's analysis in response to the study.

If the state did limit water users to their legal allocations, the water savings might not even reach Lake Powell, which is far downstream on the Utah-Arizona border. And if the water did reach the immense reservoir, it would barely do anything to refill it. The 21,400 acre-feet of water leaving Division 5 equals about 0.08% of the reservoir's total capacity of 26 million acre-feet.

Colorado officials do not need to stop the free river condition to help with the negotiations, Ullmann said. The state insists it does not need to cut its water use because it already uses less than its share, while other states in the basin are at or above their allocations.

Plus, cutting water use under free river conditions would need to be compensated, just like other conservation and fallowing programs. And these diversions are needed by Colorado's agricultural producers and other water users, he said.

"They serve a valuable purpose for Colorado's water users, primarily during a period of high flow before the streams dry out in the later summer, July through October," Ullmann said.

For Curry, the rancher and former lawmaker, the extra water during free river periods is vital to her livelihood.

There are no reservoirs above her high-elevation ranch to help pace the flow of water over the summer. She and her neighbors have to use the water when it's available, and they often use the extra water during spring runoff to moisten the deep root zones of native grass hay, the primary forage crop grown in her area.

"If they held everybody to their legal limit, it would have an impact on our ability to have a decent yield on our hay crop," she said. "If we want to lose more ag, that's a great way to do it."

Is the end near for the free river condition?

There is one clear threat to the future of the free river condition: a "compact call," when Upper Basin states would have to cut their water use to meet legal water sharing obligations.

If there's not enough water going downriver — so much so that Coloradans and others have to cut their use — then it would mean there is no unclaimed water in the state's rivers and streams.

No extra, or unappropriated, water means no free river condition, said Ullmann and water attorney David Harrison, who consulted briefly on the study.

"The constitution only protects the right to divert unappropriated water. Under the circumstances of the Colorado River — if not now, soon — it will all be appropriated," Harrison said. "There will be no unappropriated water because of future delivery requirements."

The Upper Rio Grande and Arkansas river basins have already faced this scenario and virtually never have free river conditions, Ullmann said.

State officials are adamant that the prospect of a compact call is far off. They say they're not worried about that right now.

In fact, if the compact call was authorized, it's entirely unclear what Colorado would have to do to satisfy its part of the delivery requirements. The state does not have rules and regulations to outline exactly how water users and rivers would need to be managed to satisfy the call.

To Harrison, this is a big problem. He says a compact call could happen in the near future, and the state needs to start working on the rules and regulations right now.

"We need to be able to handle it at the moment when it happens," Harrison said.