DENVER (CN) – A controversial reallocation project designed to provide water security for the growing Denver metropolis will continue as planned after the 10th Circuit Monday affirmed that the Army Corps of Engineers’ followed environmental requirements.

The 5,378-acre Chatfield State Park is located 25 miles south of Denver where the South Platte River meets Deer and Plum creeks in Littleton, Colorado. The wildlife oasis attracts 1.6 million annual visitors and is home to the infamously threatened Preble’s meadow jumping mouse as well as 375 species of birds, 15 of which are also protected.

Chatfield’s dual roles as reservoir and nature reserve clash with a $180 million plan to expand the lake by 587 acres, which opponents say is not worth losing important habitat over.

The Denver metro needs to secure 90,000 acre-feet of water by 2050 to keep up with the needs of a growing population. In 2014, the Army Corps of Engineers proposed raising the Chatfield Reservoir by 12 feet.

Once construction is complete, the expanded reservoir would account for 20,600 acre-feet of required water but at the expense of sensitive habitat. The Audubon Society of Greater Denver sued the Corps in 2014, alleging that it dismissed less-destructive alternatives.

Other project alternatives passed over by the Army Corps of Engineers included expanding other water reserves, increasing groundwater storage, using offsite gravel pits and a no-action alternative relying on current reservoirs coupled with increased water conversation efforts.

“The Corps’ decision to approve the recreation relocation and environmental mitigation plans, as modified to reduce dredge and fill, was not arbitrary or capricious,” wrote Circuit Judge Mary Beck Briscoe in a 27-page opinion affirming the state court’s December 2017 decision.

The Audubon Society further argued that the Corps wrongly combined its National Environmental Protection Act analysis with its Clean Water Act requirements.

“Even after the Corps limited its analysis to the recreation relocation and environmental mitigation plans, it sufficiently analyzed the alternatives and identified the least environmentally damaging practicable alternative,” Briscoe wrote. “During its Clean Water Act analysis, the Corps considered the plans as originally proposed by the water providers, as well as alternatives that would have involved no discharge of dredge or fill.”

Of the 38 proposed plans, the Corps argued that the Chatfield Reallocation Project would be the most beneficial and the court found no fault with their process.

While the nonprofit organization said it was disappointed in the court’s decision, executive director Karl Brummert said its members will continue to further the mission of connecting people to nature.

“As the project moves forward, Denver Audubon will continue to do what we can to protect the diverse habitats and wildlife at Chatfield State Park. We hope that much of the vegetation, groves of trees, and old growth trees will be preserved,” Brummert said.

Construction on the Chatfield Storage Reallocation Project has commenced on the western edge of the lake and is expected to be completed by 2020.

Circuit Judges Scott Matheson and Carlos Lucero also sat on the panel.