Pieter Strauss used to love hosting stargazing parties at his house in the Lakeshore Park neighborhood up Flagstaff Road southwest of Boulder. The hobbyist astronomer would fire up the barbecue and spend hours showing his neighbors the night sky through his observatory and telescopes.
Strauss’s house sits looking directly over Gross Reservoir, which provides water to Denver residents.
But when a project to significantly raise the reservoir’s dam began construction in 2022, those moments of neighborhood tranquility were lost for some residents. For Strauss the biggest impact was the bright construction lights used to keep work moving overnight.
“It became impossible to sit on the deck before sunrise and after sundown, astrophotography was impossible. They lit up the skies,” with powerful floodlights, Strauss said.
For over 20 years, residents and various environmental groups have protested the project, which suffered a series of legal blows this year. Construction on the massive dam ground to a halt in April amidst the courtroom wrangling, and subsequent decisions have cast a new level of uncertainty over large-scale water projects that propose to draw on the beleaguered Colorado River.
However, by the end of May, federal courts ruled that construction could continue due to concerns surrounding uncompleted construction and potential flooding possibilities, but that the reservoir could not be filled.
Raising the dam
Gross Reservoir’s dam is owned and operated by Denver Water. The utility built it in the 1950s, with two other building phases planned to accommodate future water needs. The current dam expansion will raise the height of the dam 131 feet, tripling the current capacity of the reservoir, and providing more water for Denver Water customers.
The construction was spurred by “a combination of demands in our system, as well as concerns about climate and concerns about the needs for greater resilience in our system,” said Jessica Brody, general counsel for Denver Water.
The need for the expansion is similar to a bank savings account, Brody said. Tripling the capacity of the reservoir is a savings account that can be drawn on in circumstances of an emergency.
“If we have an extreme drought event, we want to have more water banks that we can help smooth the impacts to our customers,” Brody said.
When the utility initially announced plans to begin moving forward with a dam expansion, residents of the area were concerned. Environmental threats and the disruptions from the massive construction project topped the list of worries. They attended meetings at town halls with county commissioners. They organized with other residents in and around Coal Creek canyon.
While some residents fought the expansion, others anticipated it. When the dam was initially constructed, the utility planned to expand further down the line.
Since construction began in 2022, residents have experienced noise and light pollution. Five neighbors have moved from the Lakeshore Park neighborhood. Pieter Strauss, at whose house they once held stargazing gatherings, was among them.
“The most valuable thing to all the people who have moved up here is that they had a quiet nature sanctuary. But then when you take that away, is it worth it?” said Anna McDermott, another resident of the area.
“We sleep with our windows open. Not one house has air conditioning, so you sleep with your windows open in the summer months,” she said. “You hear these giant backup beepers crashing, grinding all night long. Even with earplugs, I can’t sleep.”
The Environmental Group (TEG) is an organization of residents in the Lakeshore Park neighborhood and surrounding residents, focused on engaging the community in action when environmental issues arise. Along with Save the Colorado, The Sierra Club, and other environmental organizations, TEG has fought the expansion. Beverly Kurtz, former president of TEG, has worked to hold Denver Water and the companies working on the dam, Kiewit Corp. and Barnard Construction Company Inc., accountable during construction.
Heavy duty trucks are required to use a different road to access the dam rather than the paved road up Flagstaff Mountain due to fire concerns. Large semi-trucks have slid off the road due to the steep grade, which can cause traffic jams and road closures.
“At one point they had one of the two roads down this mountain closed for five months,” Kurtz said. “It wasn’t until we called the sheriff out here and he realized the safety concern that they opened the road back up.”
Legal snares slow construction
In October 2024, two years after construction began, Save the Colorado, along with other environmental groups, won a lawsuit against Denver Water. U.S. District Court judge Christine Arguello found the utility’s dam construction permit violated the Clean Water Act and the National Environmental Policy Act. At the time, construction was able to continue and Arguello ordered the groups to work out an agreement regarding damages.
In April 2025, the judge ordered a temporary halt on construction. The initial lawsuit argued that the U.S. Army Corps of Engineers, who provided the project permitting, did not fully consider climate change impacts when it approved the dam’s expansion.
A month later, Arguello ruled that Denver Water could finish construction on raising the dam, but that the reservoir could not be filled until the Army Corps reissued the permits.
“If you stop the construction of a dam when it is partially built, the dam doesn’t function as it was ultimately designed to function,” said Denver Water’s Brody. “That was a big concern of ours and the Federal Energy Regulatory Commission.”
The utility has also been ordered to not remove any additional trees surrounding the dam until the proper permits are obtained. The project proposes the removal of over 200,000 trees.
Arguello’s opinion also called into question the underlying water rights Denver Water would rely on to fill the newly enlarged reservoir when construction finished. Gross Reservoir is filled with water from the headwaters of the Colorado River, which has experienced steep declines in water supply amid a long-term warming and drying trend in the Rocky Mountains.
“The Environmental Impact Statement didn’t even look at the fact that the flows of the Colorado River are in decline. Most of the science suggests they will continue to decline further,” said Doug Kenney, Western Water Policy Program director at the University of Colorado Boulder’s Natural Resources Law Center. Acquiring new permits will require Denver Water to redefine the project’s purpose and evaluate the environmental damage, he said.
The case is more than a local water project. Diverting more water across the western slope of Colorado has created concerns for ecosystems throughout the overappropriated watershed and for communities downstream in California, Nevada and Arizona.
“It makes it more difficult to ensure that there’s sufficient flow downstream as a result,” Kenney said. “We have got to stop this practice of taking more and more water out of the upper reaches of the Colorado River because it just increases the stress on a river that is already under a tremendous amount of stress.”
By calling into question the project’s potential to have downstream impacts, the decision could add a new legal hurdle future water development infrastructure will have to clear.
“Historically, agencies in recent decades have not done enough to consider climate change in decisions,” Kenney said. Cases like this one need to happen in natural resource law more generally, he said, as they help establish precedents for future projects that could potentially put the environment at risk.
Denver Water is appealing the court decisions that bar the expansion. That could result in a reissue of the permits with a redefined purpose or a dismissal of the court rulings made earlier this year.
“We think that the district court made some misjudgements or misinterpretations when it found the Army Corps committed these errors,” Brody said.
Learning to live alongside it
Amid the stops and starts of Gross Reservoir construction, nearby residents are not ready to let go of what they used to have.
Kurtz and McDermott recall their old activities along the reservoir’s north shore. A handful of neighbors would walk their dogs everyday along the hiking trail that connected the reservoir to their neighborhood. The trail has since been widened significantly, to allow for excavating equipment. They would host Memorial Day parties along the water’s edge.
Now they minimize their excursions to the shore as much as they can. At this point they’re more than ready for construction to be completed, exhausted from the daily disruptions, explosions and drilling.
“Now clearly, when the work is done, the things which negatively impacted my life would go away. But I couldn’t last them out,” Strauss said. He recently relocated to the Boulder area. “It was just my bad luck that my golden years coincided with the worst effects of the project.”
Some residents found that the expansion project has renewed their sense of community in Lakeshore Park.
“In a weird way a lot of us have gotten even closer because we were in the battle together,” Kurtz said. “We feel like at this point we won the battle, but we’ve lost the war.”
“They will get the permits to eventually fill this reservoir following the expansion,” she said.
However, federal courts requiring the proper permits to continue construction is a win in her and TEG’s book, as it sets a precedent for any large construction processes that occur in the future. It will ensure that the proper environmental permits are obtained before construction can begin on a project.
“If nothing else, we hope that precedent still stands. Because it will help somebody else,” she said.
This story was produced by The Water Desk, an independent journalism initiative at the University of Colorado Boulder’s Center for Environmental Journalism.
