Reservoir operators on the Western Slope will ramp up releases this week to boost peak flows for the benefit of endangered fish in the Colorado River.
Known as Coordinated Reservoir Operations (CROS), five reservoirs will voluntarily send a pulse of water that arrives at the 15-mile reach near Grand Junction at the same time as the peak spring runoff. Fueled by warm temperatures this week, river flows at the Cameo gauge, just upstream of the Grand Valley, are expected to hit between 18,000 and 18,500 cubic feet per second around Saturday or Sunday, according to the Colorado Basin River Forecast Center.
Releasing the water out of reservoirs this week adds to this natural snowmelt peak and creates a cold flushing flow that clears out excess sediment built up on the cobbles favored by spawning fish. Michelle Garrison, a water resources specialist for the Colorado Water Conservation Board and who coordinates CROS, said CROS is more likely to occur in years that are average or slightly above average — not in very dry or very wet years.
“Both flushing sediment off of the spawning grounds and also providing a good temperature difference that are spawning cues for some of the fish happens at about 19,000 cfs,” Garrison said. “We typically only look at CROS if we’re projected to have a spring peak that’s close to or above 12,900 cfs and there needs to be excess inflow to the reservoirs above what they need to fill.”
The details of the timing and amount of water to be released were hashed out during a conference call Monday that included about 30 participants. In the coming days, releases out of participating reservoirs will climb and stay high for a few days before ramping back down next week.
Releases from Williams Fork Reservoir, east of Kremmling and managed by Denver Water, will increase to 800-950 cfs from about 600 cfs.
Granby and Willow Creek reservoirs, operated by the Northern Colorado Water Conservancy District, will increase releases to 400 cfs from about 240 cfs for at least 10 days.
Wolford Reservoir, which is on Muddy Creek north of Kremmling and managed by the Colorado River Water Conservation District, will ramp up releases to 550 cfs from about 490 cfs by the end of the week and stay there for about five days before dropping back down.
Green Mountain Reservoir, which is on the Blue River and operated by the U.S. Bureau of Reclamation, will increase releases to 1,500 cfs from about 400 cfs for about 10 days.
Homestake Reservoir, which is on Homestake Creek in the Eagle River basin and managed by the cities of Aurora and Colorado Springs, will not participate in CROS this year.
Fifteen-mile reach
The 15 miles of the Colorado River between Palisade and the confluence of the Gunnison River is critical habitat for four species of endangered fish: razorback sucker, humpback chub, bonytail and Colorado pikeminnow. This chronically water-short reach often does not have enough water to support healthy fish populations, especially during irrigation season in dry years. The group of diversions known as Cameo, which brings water to the Grand Valley’s farmland, can take a combined 1,950 cubic feet per second from the river — collectively, the biggest agricultural diversion from the Colorado River on the Western Slope.
CROS was established in 1995 as part of the Upper Colorado River Endangered Fish Recovery Program, which works to reestablish healthy populations of the fish by restoring habitat, growing hatchery fish and controlling nonnative predator fish. This will be the 12th year that CROS has been implemented in the 30 years since it began.
“The whole premise is that if all these reservoirs went ahead and retimed their releases, we could actually increase the effective power of the river at creating channel change and improving conditions for the recovery program,” said Victor Lee, a hydrologist with the U.S. Bureau of Reclamation. “Reclamation is fully supportive of this effort to try to improve the habitat for the endangered fish.”
David Graf, instream flow coordinator with U.S. Fish & Wildlife Service, said on Monday’s call that more than 400,000 acre-feet of water has been contributed to the 15-mile reach through CROS since the program began, which is an average of about 33,000 acre-feet each year CROS is implemented.
The last time CROS happened was in 2020. In 2021 and 2022, reservoirs were depleted from the previous dry years and didn’t have water to spare; in 2023, CROS didn’t happen because the prolonged high runoff from a big snowpack was enough of a benefit to the fish.
Ruedi releases
Ruedi Reservoir, on the Fryingpan River, will participate in CROS this week, ramping up releases in the coming days. Tim Miller, a hydrologist with the U.S. Bureau of Reclamation, which operates Ruedi, said he plans to start increasing releases Wednesday morning from the current 230 cfs. Anglers can expect flows on the Fryingpan to reach at least 650 cfs, until Monday when releases begin to ramp back down.
Miller, who expects Ruedi to fill this year, said operators may have to release excess water again in July.
“I’m pretty certain we are going to have higher-than-average releases once the tail end of the runoff comes down and we’re full,” he said. “There’s still a lot of snow.”
Water managers said even with extra water from CROS, rivers are still expected to remain well below flood stage.
This story ran in the June 4 edition of the Glenwood Springs Post-Independent and the June 7 edition of The Aspen Times and Vail Daily.