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Water Quality

Windy Gap Firming Project


In 1985, the Northern Water Municipal Subdistrict (Northern) constructed the Windy Gap Reservoir near Granby, Colorado. It removes water from the upper Colorado River and delivers it to Front Range municipalities via the Colorado-Big Thompson Project. Participants of the original Windy Gap project are Longmont, Greeley, Estes Park, Boulder and the South Platte Power Authority.

Northern’s Windy Gap Firming Project (WGFP) would add Chimney Hollow Reservoir (a 90,000 acre-foot reservoir on the East Slope) to the current system to allow delivery of more Colorado River water to Front Range municipalities. Cities that will receive water from the WGFP include Broomfield, Lafayette, Louisville, Loveland, Erie, Evans, Fort Lupton and Superior, the Central Weld County Water District, and the Little Thompson Water District. Together with the Moffat Expansion Project proposed by Denver Water, and existing diversions, WGFP may remove as much as 80% of the native flows of the upper Colorado River.

Problem: Ecological Impacts to the River

Since the construction of Windy Gap Reservoir, many ecological changes have been studied and observed throughout the upper Colorado River basin by scientists from the Colorado Division of Wildlife (CDOW) and Trout Unlimited (TU), among others. Permitting agencies, affected communities and Northern must commit to working collaboratively to create a plan to address existing ecological problems in the upper Colorado watershed and prevent future impacts caused by the expansion of this water project.  A brief summary of these ecological impacts and concerns are listed below.

  • Whirling Disease and Invasive Species. Multiple studies by the Colorado Division of Wildlife (CDOW) and Trout Unlimited (TU) confirm that the parasite that causes whirling disease, Myxobolus cerebralis, has led to the catastrophic loss of wild rainbow trout in the upper Colorado basin. These studies have concluded that Windy Gap Reservoir was the major culprit in producing the trout-infesting triactinomyxon spore linked to this disease. Proliferation of other harmful aquatic species, such as didymo (“rock snot”), are also documented, serious problems.
  • High Temperatures. Grand Lake and the upper Colorado River and its tributaries below Windy Gap Reservoir currently experience water quality problems including stream temperatures that exceed state standards for coldwater aquatic life – standards designed to protect species such as trout. Indeed, the State Water Quality Control Commission has placed the Colorado River on its list of “impaired waters” due to these temperature problems. The high stream temperatures occur when flows are low in the summer and early fall; further diversions may push temperatures even higher and for longer periods of time.
  • Algae. Oxygen-robbing algae blooms are already a documented problem in the upper Colorado River and Grand Lake. Without adequate concentrations of oxygen in the water, fish and macroinvertebrate populations that fish depend on, like the stone fly, cannot survive.
  • Sediment. Empirical data show excess sediment in the Colorado River due to inadequate “flushing flows.” Flushing flows are produced by large quantities of fast-moving water, especially during periods of runoff and rainy seasons. Sediment that remains in the river can suffocate and kill the fragile macroinvertebrate populations, such as stonefly, that trout depend on for food, and damage spawning grounds where trout reproduce and lay their eggs. With further reduced flushing flows, this problem is expected to get worse.
  • Macroinvertebrates. Stonefly populations, an important source of food for trout, have significantly declined downstream of Windy Gap Reservoir and in some areas, have been effectively eliminated; increased diversions could exacerbate this downward trend.
  • Native fish. The populations of native sculpin have significantly declined as their relative abundance ranges between zero and five percent at sampling sites on stream reaches downstream of the main stem impoundments at Granby, Willow Creek, Windy Gap and Williams Fork reservoirs. Increased diversions may exacerbate this downward trend.
  • Trout. The CDOW has identified significant declines in trout size and abundance compared to historic norms. One example is the trout population in the Kemp-Breeze State Wildlife Area near Parshall, where fewer large trout are found compared to surveys conducted prior to construction of the Windy Gap Project.  Recent surveys have also shown that those larger trout that are found below Windy Gap are in poorer condition than those further downstream where Windy Gap impacts are partly offset by inflows from other tributaries to the Colorado.

Solution: Avoiding New Impacts, Fixing the Old

Removing additional water from the upper Colorado River will likely exacerbate currently compromised conditions by creating persistent low-flows during critical summer months and eliminating peak (flushing) flows. To date, satisfactory mitigation for the past and potential project impacts have not been proposed by Northern Water. If the Wildlife Commission and other permitting agencies approve Windy Gap Firming Project, measures need to be in place that acknowledge existing impacts and prevent future impacts to river ecosystem health. Northern Water must commit to the following mitigation measures as conditions of the permits issued for this project:

  • Maintain adequate “flushing flows.” Currently, the Colorado River below Windy Gap Reservoir receives only 450 cubic feet per second of flushing flow in accordance with the existing agreement. Flushing flows are produced by large quantities of fast-moving water, especially during periods of runoff and rainy seasons. Flushing flows are required to clean out fine sediment from river beds in order to maintain healthy macroinvertebrate populations and spawning grounds where trout reproduce and lay their eggs. The inability of these minimal flushing flows to remove sediment from gravel beds is a huge concern. The CDOW has recommended minimum flushing flows below Windy Gap Reservoir. Flushing flows have also been recommended by the CDOW and by Grand County’s Streamflow Management Plan.
  • Keep the river cool when it’s hot. No project diversions should be allowed when stream temperatures reach state standards to protect trout fisheries (about 64° F); or when making the diversions will lead to higher temperatures than under the state standards. Means to increase existing flows during critical summer and early fall months should be found.
  • Reconnect the Colorado River.  Dams have impacts that go beyond flow depletion; they also block downstream passage of the “bed load” – gravels and cobbles that help maintain healthy habitat – and upstream passage of fish and other aquatic life.  The Northern District has proposed a study of building a bypass around Windy Gap to reconnect the Colorado River should be studied.  If the study documents that a bypass will benefit the river, they should also provide the funds needed to build it.
  • Monitor and take responsibility. Even with these proposed specific measures, the reality is that science cannot at this point predict the complex interactions and impacts of removing over 70% of the native flows from a river. Water providers must make a commitment to monitor stream conditions and wildlife closely in order to detect potential declines in ecosystem health. If negative impacts are observed, then providers need to take steps to address potential problems by changing how much and when they remove water from the Fraser and Colorado River. This process is referred to as “adaptive management.”

Maximizing Municipal Water Conservation

Many of the cities and municipalities that will receive water from the Windy Gap Firming Project could do more to meet their increased water needs through more aggressive conservation measures, delaying the need for expensive and ecologically harmful water projects. These measures include implementing a tiered rate structure, incentives for irrigation improvement projects, and reducing the system’s water loss.

Taking Action

Colorado TU is working diligently to protect the Upper Colorado River. Learn more about what we are doing and get involved by visiting