Chimney Hollow Reservoir

Official account for the proposed Chimney Hollow Reservoir, which is being by built by @northern_water Municipal Subdistrict.

[Chimney Hollow Reservoir @ChimneyHollow]

Two years ago this month, the clay embankment of the saddle dam began on the southern end of the reservoir. The saddle dam allows the reservoir to hold the necessary 90,000 acre-feet of storage by increasing the capacity of the reservoir by about 30 percent.

[Chimney Hollow Reservoir @ChimneyHollow]

Even though some water has been placed in the reservoir, no water will be released or delivered to Chimney Hollow project participants until assessments are complete, and a mitigation plan is in place to ensure a safe water supply.

[Chimney Hollow Reservoir @ChimneyHollow]

The initial fill of Chimney Hollow Reservoir has concluded, and the reservoir currently has about 1,500 acre-feet of water—less than 2 percent of the reservoir's full capacity of 90,000 acre-feet. Read more about the initial fill at https://t.co/WaxdbfiFWz.

[Chimney Hollow Reservoir @ChimneyHollow]

Northern Water is committed to providing a high-quality raw water supply to Northeastern Colorado and will continue to monitor all water that is delivered from our projects to our communities.

[Chimney Hollow Reservoir @ChimneyHollow]

Water quality and clarity in Grand Lake and the Three Lakes System have long been a priority, and the success of those efforts has accelerated in recent years, thanks to a variety of collaborations with numerous entities in Grand County and beyond. https://t.co/D3kTpEZQ5M

[Chimney Hollow Reservoir @ChimneyHollow]

Northern Water will move approximately 1,500 acre feet of water into Chimney Hollow Reservoir starting mid-April. During this time, additional water quality data will be collected and used to evaluate the performance of model simulations. Learn more at https://t.co/WaxdbfiFWz.

[Chimney Hollow Reservoir @ChimneyHollow]

FROM THE ARCHIVES: It's been four years since crews began the excavation on the inlet/outlet tunnel. In this video, Peter Turlington with Barnard Construction explains the importance of this critical infrastructure and the steps it took to build it. https://t.co/7oDFoUdSaH

[Chimney Hollow Reservoir @ChimneyHollow]

Although the discovery of uranium is a setback to initial plans, it is an issue that can be safely managed and is expected to decrease over time. Chimney Hollow remains a valuable part of securing water supply needs for Northern Colorado and its future.

[Chimney Hollow Reservoir @ChimneyHollow]

While we are gathering and analyzing information to understand the full scope of the presence of uranium at Chimney Hollow Reservoir, we are evaluating a range of mitigation options.

[Chimney Hollow Reservoir @ChimneyHollow]

Hard to beat this view—sunshine, fresh air and a project shaping the future.

[Chimney Hollow Reservoir @ChimneyHollow]

Northern Water carries out extensive water quality monitoring on both sides of the Continental Divide to track changes in water quality in the Colorado-Big Thompson and Windy Gap projects. Protecting the quality of our source water is a responsibility we take very seriously.

[Chimney Hollow Reservoir @ChimneyHollow]

Did you know? Pikes Peak, located about 10 miles west of downtown Colorado Springs, is visible from the Chimney Hollow main dam on a clear day. Completed last year, the main dam stands at 350 feet tall and is the largest new dam built in the United States in the last 25 years.

[Chimney Hollow Reservoir @ChimneyHollow]

We are working closely with experts to get a full understanding of the uranium at Chimney Hollow Reservoir, which includes water quality testing, data collection, modeling and more.

[Chimney Hollow Reservoir @ChimneyHollow]

A weather station has been installed at Chimney Hollow Reservoir west of the main dam. The station provides temperature, relative humidity, wind speed, wind direction, solar and barometric pressure. Rain data will be available from March 1 – Oct. 1.

[Chimney Hollow Reservoir @ChimneyHollow]

It's been a while since we've posted a photo from the eastern ridge of the valley just above the main dam. This photo, taken Monday, Jan. 12, looks quite a bit different than past updates. The site is quiet and cleaned up, and all that remains are some minor punch list items.

[Chimney Hollow Reservoir @ChimneyHollow]

Chimney Hollow was built to firm the water rights associated with the Windy Gap Project, first proposed in 1967 by the cities of Boulder, Estes Park, Fort Collins, Greeley, Longmont and Loveland. Learn more at https://t.co/4ez1I2kDE5.

[Chimney Hollow Reservoir @ChimneyHollow]

Marking a major milestone, 2025 was the year construction wrapped up on Chimney Hollow Reservoir—the tallest new dam built in the United States in the past 25 years. Read the full recap at https://t.co/os0RW7YJo0

[Chimney Hollow Reservoir @ChimneyHollow]

This project will utilize the water rights associated with the existing Windy Gap Project, which has been delivering water since 1985. Chimney Hollow will provide the additional storage needed to make the Windy Gap Project a more-reliable delivery system.

[Chimney Hollow Reservoir @ChimneyHollow]

In late November, the Northern Water Municipal Subdistrict Board of Directors and project participants gathered on site to commemorate the completion of construction at Chimney Hollow Reservoir.

[Chimney Hollow Reservoir @ChimneyHollow]

Every Monday during construction of the Chimney Hollow Reservoir Project, we posted a progress photo from a camera nestled up high on the eastern ridge of the valley. Here is the final timelapse video. Enjoy four years of construction in about 3.5 minutes! https://t.co/h4vPvTDgTs