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Tallest U.S. dam in the last two decades nearing completion in Northern Colorado

Tallest U.S. dam in the last two decades nearing completion in Northern Colorado
Tallest U.S. dam in the last two decades nearing completion in Northern Colorado 02:43

One of the largest dams built in the United States in the last two decades is one year away from completion, a dam that will help supply water to Northern Coloradans for decades to come. 


The Chimney Hollow Reservoir project is underway in the Foothills west of Loveland, and it's expected to be completed and retaining water by summer of 2025.

"We've been planning this project since the late 1990s," said Joe Donnelly, principal project manager for Northern Water.

The project is designed with the future in mind. Northern Colorado is one of the fastest growing regions in the state. With that, communities in Northern Colorado are collaborating to secure water resources for their future residents.

"The population of Colorado is growing and has been growing for a long time. Especially in Northern Colorado, where eight of the 10 fastest growing communities in the state are in our service area," Donnelly told CBS News Colorado's Dillon Thomas.

The dam, which will be the fourth largest in Colorado when completed, is now 50% completed.

"This is a new 350-foot-tall rock-filled dam. This is the tallest new dam built in all of the United States in the last 20 or 25 years," Donnelley said.

The dam will be only the second asphalt-core dam built in the United States, although the construction type is common in Europe.

The rocks building the dam are locally sourced, coming from the ground that will soon be covered by the water in the reservoir. Each day, crews are transporting more than 62,000 tons of rocks from the quarry to the dam.

"So it also makes (this project) one of the largest mining operations in the state of Colorado," Donnelly said.

Donnelly, a Loveland native, said this project is a highlight of his career.

If everything goes to plan, Northern Water plans to start filling the reservoir with water in the summer of 2025. They expect it will take three years to completely fill the reservoir, although that is dependent on Mother Nature.

The water comes from the Western Slope, originating in the Colorado River. Because those on the Eastern Slope will be taking the water, Northern Water has invested nearly $90 million in the Colorado River and the Western Slope's water resources to help offset their impact.

In the end, 12 different municipalities north of Denver will be able to access the water in Chimney Hollow Reservoir. 

Larimer County helped purchase the property. When the construction is completed, Larimer County will take over operating the recreation and open spaces in and around the reservoir.

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