Colorado reservoirs coordinate to provide peak flows for endangered fish |

Colorado reservoirs coordinate to provide peak flows for endangered fish

Alli Langley
Danielle Tremblay, seasonal fisheries technician for Colorado Parks and Wildlife, holds a Colorado pikeminnow, one of four species of fish found only in the Colorado River system and protected under the Endangered Species Act. The pikeminnow was first listed as endangered in 1967. Valued as food by early settlers and miners, the fish may reach 6 feet in length, weigh 80 pounds, live 40 years and swim more than 200 miles to spawn in the late spring and early summer.
Courtesy of Colorado Parks and Wildlife |

SUMMIT COUNTY — For much of the spring, operators of reservoirs above the Upper Colorado River said the skies had not been generous enough to allow them to release surplus water that would help endangered fish.

U.S. Bureau of Reclamation hydrologist Ron Thomasson, who manages Green Mountain Reservoir operations in northern Summit County, said as much about the warm, dry weather affecting snowpack and streamflows at the county’s 22nd annual State of the River in early May.

But heavy May rains changed that.

Colorado River Water Conservation District general manager Eric Kuhn recently called the precipitation miraculous.

“We hydrologists were just so happy with all this rain.”Jana MohrmanU.S. Fish and Wildlife Service hydrologist, Upper Colorado River Endangered Fish Recovery Program

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For the first time in five years, the district collaborated with the Bureau of Reclamation and Denver Water to mimic natural spring runoff and peak-river flows.

That’s about the opposite of what reservoir operators typically do as they try to store water for times of drought, prevent floods and generally even out flows throughout the year, said Jana Mohrman, the U.S. Fish and Wildlife Service hydrologist with the Upper Colorado River Endangered Fish Recovery Program.

The three reservoir operators finished a conference call Monday and made the decision to participate in the Coordinated Reservoirs Operations Program with their six reservoirs starting that afternoon.

“We hydrologists were just so happy with all this rain,” Mohrman said. “The Front Range got a lot more, but, still, the Upper Colorado was fortunate.”


The Upper Colorado River Endangered Fish Recovery Program is a cooperative partnership of local, state and federal agencies, water developers, power customers and environmental groups established in 1988 with the goal of recovering four endangered fish species — the humpback chub, razorback sucker, bonytail and the Colorado pikeminnow — while water development continues in accordance with federal and state laws and interstate compacts.

The group created the Coordinated Reservoir Operations program in 1995 to enhance spring peak flows in a section of the Colorado River upstream of Grand Junction determined critical to the survival of the four endangered fish, which are only found in the Colorado River system.

Mohrman said the fish depend on the flows peaking in the spring.

The razorback sucker, for example, spawns when the water starts to rise, and the rush of runoff cleans the river’s gravel. Meanwhile, the pikeminnow spawns when the water starts to drop because its young can safely grow in the backwater that forms.

In years with sufficient snowpack, surplus inflows to the reservoirs can be passed downstream to benefit the fish without impacting reservoir yield.

In 2011 and 2014, wet conditions caused streamflows in certain parts of the Upper Colorado River Basin to flood or approach flood levels, so the reservoir operators did not coordinate to peak flows.

On the other hand, extremely dry conditions in 2012 and 2013 meant reservoirs did not have surplus inflows to contribute while prioritizing human water supplies.

“You just have to work within nature,” Mohrman said.

Besides augmenting flows to mimic a natural peak, she said, the fish-recovery program also stocks native species and removes non-native species. She said all of the program’s partners feel the group has made progress in its work on water development and conservation.

“We feel like the fish flows have been recognized and are for the most part in place,” she said.

The group’s biggest stumbling block right now, she said, are the non-native fish like smallmouth bass, northern pike and walleye that aggressively compete with the native fish. The program is now concentrating more time and money on removing the invasives.


In Summit County, an unexpected increase in late-season snowpack allowed the Bureau of Reclamation to increase Green Mountain Reservoir outflows in recent weeks to the maximum power plant capacity of 1,500 cubic feet per second. Green Mountain won’t increase its outflows further as part of coordinated operations.

Denver Water, which operates Dillon Reservoir and sends releases toward Green Mountain, also operates the Williams Fork Reservoir in Grand County. The utility was releasing about 270 cfs from Williams Fork on Monday, and officials said they could raise those releases if inflows increased last week but would not exceed 500 cfs.

Also in Grand County, the Wolford Mountain Reservoir, operated by the Colorado River Water Conservation District, increased outflows from about 450 cfs to roughly 600 cfs this week.

Granby Reservoir, operated by the Bureau of Reclamation and Northern Colorado Water Conservancy District, increased releases from 1,000 cfs to about 1,800 cfs this week. The sixth reservoir involved, Ruedi Reservoir, is operated by the Bureau of Reclamation, which increased Ruedi’s releases from 200 cfs to 650 cfs.

The Colorado Basin River Forecast Center incorporates these reservoir operations into its streamflow forecasts and predicted that flows at Cameo will be about 15,000 to 16,000 cfs through Wednesday.

More detailed information about forecasted streamflows in the Colorado River basin are available on the CBRFC website at, where a map-based interface allows viewing of hydrographs that show recent, current and anticipated flows.

For more information about the Upper Colorado River Endangered Fish Recovery Program, visit http://www.colorado

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