Colorado leaders on Wednesday endorsed Denver Water’s $380 million project to divert more of the state’s allocated share from the oversubscribed Colorado River, mostly during wet years, and store more in an expanded reservoir to slake growing Front Range thirsts during dry years.

This formal backing completes the state’s environmental reviews for the Moffat project, 13 years in the making, clearing the way for construction — if remaining federal permits are issued. Denver Water and opponents from Western Slope towns and nature groups reached a compromise aimed at enabling more population growth while off-setting environmental harm.

It is a key infrastructure project that will add reliability to public water supplies and protect the environment, Gov. John Hickenlooper wrote in a letter to Denver Water manager Jim Lochhead.

It “aligns with the key elements of Colorado’s Water Plan,” Hickenlooper wrote. “Denver Water and its partners further our shared vision for a secure and sustainable water future while assuring a net environmental benefit in a new era of cooperation.”

Denver would siphon 10,000 acre-feet a year, on average, more water out of Colorado River headwaters, conveying it eastward under the Continental Divide through a tunnel for more than 20 miles to an expanded Gross Reservoir southwest of Boulder. By raising that reservoir’s existing 340-foot dam to 471 feet, the project would increase today’s 41,811 acre-feet storage capacity by 77,000 acre-feet — more than doubling the surface area of the reservoir.

More than 50 million people in western states rely on the Colorado River for water, and a 1922 interstate compact allocates more water to states than the river contains. Demand exceeds supply. Water in reservoirs serving people in Nevada, Arizona and California this year fell to record low levels.

For more than a decade, Denver Water has been seeking permits, including federal approval for construction affecting wetlands and to generate hydro-electricity at the dam.

“During dry years, we won’t be diverting water. It is a relatively small amount of water. … It is a water supply that Colorado is entitled to develop,” Lochhead said in an interview.

The increased storage capacity “allows us to take water in wet times and carry it over through drought periods. It gives us operational flexibility on the Western Slope. … Having this additional storage enables that flexibility.”

Colorado leaders’ formal endorsement follows a recent Colorado Department of Public Health and Environment decision to issue a water quality permit for the project, certifying no water quality standards will be violated. Hickenlooper has directed state officials to work with federal water and energy regulators to expedite issuance of other permits. Denver Water officials said they expect to have all permits by the end of 2017, start construction 2019 and finish by 2024.

“The state’s responsibility is to ensure we do the right thing for Colorado’s future, and this project is vital infrastructure for our economy and the environment,” Hickenlooper said in a statement. “The partnerships and collaboration between Denver Water, the West Slope and conservation organizations associated with this project are just what the Colorado Water Plan is all about.”

Save the Colorado River director Gary Wockner said he’s geared up to fight the project in court. “The Gross Dam project is reckless and will further drain and destroy the Fraser and Upper Colorado River as well as cause irrevocable damage to the environment and citizens of Boulder County.”

But Trout Unlimited and other conservation groups call the project a realistic compromise considering the rapid population growth along Colorado’s Front Range.

“If the state needs to develop more water, they need to do it in a less-damaging, more responsible way — as opposed to going to the pristine headwaters of the South Platte River, which is what the Two Forks project was going to do,” TU attorney Mely Whiting said.

“We’ve put things in place that will make Denver Water be a steward of the river,” Whiting said. The agreement hashed out between Denver Water and conservationists “does not specifically say they have to tweak the flows to help the environment. It does say they have to monitor, for water temperature and macroinvertebrates. And if there’s a problem, they are responsible for figuring out why and they need to do something about it. It does not say exactly what they have to do but they have to fix any problem.”