Army Corps investigating Grizzly Reservoir releases that discolored river 

A federal agency is investigating whether July releases from Grizzly Reservoir, which temporarily turned local rivers bright orange, were not in compliance with the federal Clean Water Act. 

Twin Lakes Reservoir & Canal Co., which operates Grizzly Reservoir, drained the reservoir this summer so it could complete repairs to the dam and outlet works. Officials said the drawdown would happen slowly to avoid releasing a lot of sediment from the bottom of the reservoir into Lincoln Creek. But, nevertheless, on July 16, Lincoln Creek and the Roaring Fork River turned orange, alarming Aspen residents and visitors. 

Wendy Huber, chair of the Pitkin County Healthy Rivers board, was near the John Denver Sanctuary in Aspen that morning and was surprised to see the river look like carrot juice. 

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“It was unbelievable, the discoloration,” she said. “You see all the tourists who are wandering around and they were standing on bridges going, ‘What’s happening?’ And as chair of Healthy Rivers, I thought, ‘I wonder what is happening. This is terrible.'” 

A July 1 news release from Pitkin County said that temporary discoloration of Lincoln Creek and the Roaring Fork River was a possibility as the reservoir was drawn down, but the severity was still shocking to some Pitkin County officials.

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“I think many of us were very surprised we saw something like that happen,” Huber said.

Now, the U.S. Army Corps of Engineers is looking into whether that discoloration could have qualified as flushing sediment that would have needed a permit under section 404 of the Clean Water Act. According to regulatory guidance from USACE, “the discharge of substantial quantities of accumulated bottom sediment from or through a dam into downstream waters constitutes a discharge of dredged material (and possibly of fill material) that requires a CWA Section 404 permit.” 

An Army Corps permit is needed for sediment releases when the release is not part of normal operations and the sediment accumulates to such an extent that it has the effect of fill material being discharged into the stream, said Ben Wilson, senior project manager for the Army Corps.

“Our review is currently focused on determining if the sediment release had the effect of fill material being discharged into the stream,” Wilson said.

In other cases involving sediment releases from reservoirs that required such a permit, the reservoir operators were required to release less-turbid water to mobilize and disperse the sediment, but in this case, the corps will assess the need for similar mitigative measures only if they determine that the release of sediment was a regulated activity, Wilson said.

Twin Lakes contractors installed sediment traps below the reservoir, which consisted of hay bales and tarps, but they did not capture all of the extremely fine sediment. 

The Roaring Fork also ran orange in 2015 during a fast emergency drawdown of Grizzly Reservoir. Twin Lakes President Alan Ward said they were hoping to avoid a similar occurrence this time by drawing down the reservoir slowly.

“We knew that we were not going to quickly drain the reservoir,” Ward said. “We didn’t have any operational experience to know if we just let it out really slowly, what would happen. We were hopeful that it wouldn’t move any sediment, but we really didn’t know.” 

Twin Lakes operators drew down the reservoir primarily through the Twin Lakes Tunnel that goes across the Continental Divide and feeds into the Arkansas River basin. But there was about an additional 60 acre-feet remaining below the tunnel intakes, and the only way to drain it was through the dam and down Lincoln Creek.

Awaiting water quality test results  

In addition to the sediment issue, the other big question on the minds of water managers is what was in the discolored water and was it a threat to public health. Pitkin County issued an alert the afternoon of July 16 encouraging anyone recreating in the river to exercise additional caution and not ingest the water, and to keep pets out of the water. 

Scientists at the Roaring Fork Conservancy had known that there could be impacts to water quality from the reservoir drawdown this year, and they received a $15,000 grant from Healthy Rivers to do sampling of Lincoln Creek at locations below the reservoir, including on July 16 and 17. RFC water quality program manager Chad Rudow said he is still waiting on the results of that sampling. 

Water quality in Lincoln Creek has long been a concern because of high concentrations of metals, which may be increasing. A 2023 Environmental Protection Agency report found that Lincoln Creek above Grizzly Reservoir is toxic to fish, with high concentrations of aluminum and copper. Experts say the source of contamination is a naturally occurring “mineralized tributary” near the ghost town of Ruby that flows into Lincoln Creek. The contamination may be exacerbated by climate change as temperatures rise. 

In addition to the Roaring Fork Conservancy, four other entities are conducting water quality sampling on Lincoln Creek this summer: Pitkin County Environmental Health; the U.S. Forest Service; Colorado Parks and Wildlife; and the Institute of Arctic and Alpine Research at University of Colorado Boulder. The Lincoln Creek Workgroup, led by Pitkin County, has hired consultant LRE Water to review the existing EPA report and other data, make a site visit, and comment on the water quality sampling plans of the five different entities. 

Future mitigation

Pitkin County officials are now turning toward the future and looking at how incidents such as these can be avoided or mitigated in the future. 

“A number of us have talked about having a debrief,” said Pitkin County Environmental Health director Kurt Dahl. “I think there’s some agreement of talking through what happened, what can we learn and what can be done in the future.”

Having mitigation measures in place for future reservoir releases may be important, especially since Ward said the repairs to the reservoir are running behind schedule, and although they still hope to finish work this year, the contractors may have to come back and complete the work next summer at the high alpine site. The reservoir will be refilled before winter, Ward said. 

“The only way to put the liner on is with an empty reservoir,” he said. “So, we’d have that same risk [of sediment release] again next year. I think what we learned is it may be unavoidable to have at least some level of sediment mobilized during the drawdown.”

Grizzly Reservoir is part of the Independence Pass Transmountain Diversion System, a highly engineered collection system that takes water from the headwaters of the Roaring Fork River basin and brings it to Front Range cities and farms. Water providers in Colorado Springs, Pueblo and Aurora own 95% of the water from this system. 

Earlier this summer, Pitkin County officials had been happy that the reservoir maintenance was going to result in more water for the Western Slope. The Twin Lakes Exchange Agreement did not take place this year, resulting in an additional 3,000 acre-feet flowing down Hunter Creek. And creeks that normally feed Grizzly Reservoir — New York, Brooklyn and Tabor — were also allowed to run down Lincoln Creek, adding to its flow. Every little bit helps in a system where 40% of the headwaters are diverted to the Front Range.

But for Pitkin County Healthy Rivers, an entity charged with maintaining and improving water quality and quantity, the extra boost to local rivers this year may not have been worth it if it came with a toxic slug of water from the bottom of Grizzly Reservoir.

“We derived a little bit of benefit to quantity because it didn’t flow to the Front Range,” Huber said. “But it begs the question: Do we want the quantity with the lack of quality?”

Aspen Journalism is a nonprofit, investigative news organization covering water, environment, social justice and more. Visit AspenJournalism.org for more information.

Heather Sackett is the managing editor at Aspen Journalism and the editor and reporter on the Water Desk.