A group of environmental groups Thursday filed a lawsuit in U.S. District Court in Denver to block the Windy Gap Firming Project, a project being developed by the Northern Colorado Water Conservancy District that would divert water from the Colorado River to the northern Front Range, beginning around 2022 or 2023.

The environmental groups suing the conservancy district include the Save the Colorado and Save the Poudre River coalitions, WildEarth Guardians and Waterkeepers Alliance. They are represented by the University of Denver’s  Environmental Law Clinic.

The existing Windy Gap project consists of a diversion dam on the Colorado River, about 10 miles west of Granby. The dam creates the 445-acre-foot Windy Gap Reservoir, a pumping plant and a six-mile pipeline to Lake Granby.

During wet periods, when Lake Granby is full, the pump plant cannot operate due to lack of reservoir storage. The Windy Gap Firming Project would build a new reservoir, known as Chimney Hollow, to be located near Carter Lake west of Loveland. Once completed, Chimney Hollow could hold up to 90,000 acre-feet of water. An acre-foot of water is 326,000 gallons, about the amount of water used by two families of four in a year.

The Chimney Hollow reservoir received its final approval from the U.S. Army Corps of Engineers last May. Construction is expected to begin in 2019, with an estimated cost of $400 million, paid for by the 12 water providers and municipalities the reservoir would serve.

In a statement, the coalition said the Colorado River in Grand County “already loses 70 percent of its flow by the time it reaches the town of Hot Sulphur Springs. If the Windy Gap Firming Project is built – along with Denver Water’s proposed Moffat Project – that loss would reach 80 percent.”

Gary Wockner of Save the Colorado said that draining 80 percent of the water from the Colorado “is ecological annihilation. If you try to further dam and drain the Colorado River or its tributaries, we will do everything we can to stop you.”

Wockner added that water agencies that need more water need to focus on conservation, water recycling and leasing or buying water from farmers.

The coalition also blasted the U.S. Bureau of Reclamation and the Corps for what the coalition called an “inadequate” environmental review of the project. That included a lack of examination of alternatives to the project, according to the announcement.

But Brian Werner, a spokesman for Northern Water, told Colorado Politics that the Windy Gap Firming Project has the buy-in of environmental group Trout Unlimited, as well as support from Grand County. The project “took years of delicate negotiations, including times when we didn’t even want to look at each other, to get to point that Grand County and Trout Unlimited are supportive.”

Werner added that there’s never been another water project in the history of Colorado that had support from the county of supply,  Grand County, an endorsement from a major environmental group, and an endorsement from the governor.

“We put together one of the most robust mitigation plans ever done,” he said. “The Colorado River below Windy Gap is better off with the project than it is today.”