April 10, 2025

Chimney Hollow Reservoir to Boost Region’s Water Resiliency

When Stephen Long and his team of Army explorers made a visit to Northern Colorado in the summer of 1820, the view was grim. By early July, when Long and his men camped near the mouth of the Little Thompson River, the spring melt had concluded, leaving the Little Thompson and South Platte as muddy channels under a baking sun.

In his map, he labeled this area as the “Great Desert.”

Fast forward 100 years, and settlers had transformed this region into an agricultural powerhouse – albeit one that was still short of water. Some years, there was plenty of water to get to reservoirs, ditches and fields to bring a crop of sugar beets to maturity. About one-third of the time, however, the crops wilted because of the lack of water.

In 1937, Northern Water was created to help the U.S. Bureau of Reclamation to manage (and pay a share of) the Colorado-Big Thompson Project, which added supplemental water to the region to ensure crops could make their way to market.

When the project was completed in 1957, Northern Water delivered 97 percent of the project’s water to agricultural operations in the region, and this area took off. Water from the project also helped communities diversify their economies, attracting employers such as Hewlett-Packard, IBM and Eastman Kodak. As those communities saw water being transferred from farms to local municipal and industrial use, their leaders saw the need for an additional water supply just for the cities. From that was born the Northern Water Municipal Subdistrict and its showpiece, the Windy Gap Project.

The Windy Gap Project collects water below the Fraser and Colorado rivers into Windy Gap Reservoir, which was built in 1985. From there, that water is pumped up into Lake Granby while it awaits distribution to municipal users. Project builders recognized that when Lake Granby was full there would be no place to store the Windy Gap Project water, but the need for additional storage was not immediate.

In 2002, a drought gripped Colorado’s Front Range, forcing those communities receiving Windy Gap Project water to address the need for storage of that water beyond Lake Granby. From that came an alternatives analysis to determine the best place to build a reservoir, and the answer was clear: Chimney Hollow.

The Windy Gap Firming Project (of which Chimney Hollow Reservoir is the major component), was reviewed and approved by federal and state regulators under the National Environmental Policy Act. A decades-long process to earn the required permits will result in robust mitigation, enhancements and protection for fish, wildlife and the environment, to address the project's impacts. 

Construction at the reservoir began in August 2021. Completion is planned in summer 2025, with the reservoir opening to public recreation under the Larimer County Department of Natural Resources in 2027.

As part of the Windy Gap Firming Project’s permitting phase to build Chimney Hollow Reservoir, the historical impacts of the original Windy Gap Project were also evaluated, including the loss of river connectivity following construction of the Windy Gap Reservoir dam on the Colorado River. 

To minimize Windy Gap dam’s impact on aquatic habitat and species in the Colorado River, the Municipal Subdistrict, which owns and operates the Windy Gap Project, agreed to decrease the reservoir’s footprint and construct the Colorado River Connectivity Channel (CRCC) around the reservoir capable of passing water, fish and sediment, thereby reconnecting two segments of the Colorado River.

CRCC construction activities began summer of 2022 and were completed in fall 2024. A ribbon cutting ceremony took place on Oct. 15, 2024, with many of the project partners taking part in the event. 