District Manager Weighs in on Gross Reservoir Expansion Project

The Gross Reservoir Expansion Project aims to raise the dam by 131 feet, increasing the reservoir’s capacity by 77,000 acre-feet. This expansion is intended to enhance water security for the Front Range, particularly in the face of climate change-induced challenges such as droughts and wildfires. Construction began in 2022, with the first phase of dam-raising completed by the end of 2024.

However, the project has faced opposition from environmental groups and local residents concerned about its ecological impact. Legal battles have been ongoing since 2018, focusing on alleged violations of environmental laws and the adequacy of the permitting process.

The most recent legal hindrance occurred on April 3, 2025, when U.S. District Court Judge Christine Arguello ordered Denver Water to stop construction on the Gross Reservoir Expansion Project. The ruling cited deficiencies in the federal environmental permitting process, particularly concerning the U.S. Army Corps of Engineers’ 2017 approval under the Clean Water Act.

The following information was provided by Denver Water. District Manager, Cynthia Lane, voices support for the Gross Reservoir Expansion on behalf of the 61 partner distributors of Denver Water.

Gross Reservoir Expansion Project gains support

Denver and state leaders are weighing in on an April 3 ruling that halted construction on Denver Water’s Gross Reservoir Expansion Project, with Denver’s mayor calling it “deeply concerning” and Colorado’s governor seeking to “fully understand the (decision’s) impact on Coloradans and our precious water supply.”

The expansion project, which entered the permitting process following Colorado’s devastating 2002 droughts, will nearly triple the storage capacity of the reservoir northwest of Denver by raising Gross Dam, work that is nearly 2/3’s complete.

Construction on the project to raise the existing Gross Dam by 131 feet as of April 8, 2025. Photo credit: Denver Water.

The project addresses the critical need to shore up a reliable water supply for 1.5 million people in Denver and surrounding communities. It does so by providing badly needed water storage capacity on the north side of Denver Water’s system to guard against drought, wildfire, and other natural and human-caused disasters.

However, federal Judge Christine Arguello, with the U.S. District Court for the District of Colorado, issued a ruling April 3 that halted construction on the project, despite 23 years of careful planning and permitting involving Denver Water and multiple local, state and federal agencies. Denver Water is appealing the ruling.

Understanding how important this project is to Denver Water’s customers and the metro area, Denver and state leaders are weighing in on the project and the April 3 ruling:

Colorado Governor Jared Polis

“We are reviewing this decision to fully understand the impact on Coloradans and our precious water supply. This decision comes as the project is more than halfway completed, and after decades of work, it is important that there is a resolution that protects this water resource for Coloradans.” (April 8, 2025, on X(opens in new window)(opens in new window)(opens in new window) with a link to a Fox31 news story(opens in new window)(opens in new window)(opens in new window) about the April 3 court ruling.)

Cynthia Lane, Manager of the Platte Canyon, Southwest Metro, Columbine and Bow-Mar water and sanitation districts and Chair of the Denver Water Distributor Forum 

“On behalf of the 61 distributor districts served by Denver Water, and the 770,000 people we serve, we share with Denver Water a collective, steadfast and decades long commitment to responsibly securing a reliable, regional water supply by way of the Gross Reservoir Expansion Project. The recent court ruling to halt the project — decades into the making through diligent planning and permitting — puts our customers and the entire metro area at unnecessary risk at a time when water security is becoming even more critical.

With our watersheds and neighborhoods already under the year-round threat of devastating wildfires and our weather patterns increasingly marked by uncertainty and extremes, the Gross Reservoir expansion provides our neighbors and customers with the best protections now, while also supporting our vibrant communities for decades to come. Knowing this project has been subject to years of rigorous, repeated and diligent review at local, state and national levels, we believe this critical project must move forward to completion — for the benefit of our customers and our communities.”