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Instream Restoration Riparian Restoration Fish Passage
High Elevation Dam Removals in Rocky Mountain National Park Rocky Mountain National Park, Colorado

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The following information was taken from “Fisheries and Aquatic Management, Rocky Mountain National Park” (USFWS, 2001) and “Restoration of Three High Altitude Lakes Inundated by Dams within Rocky Mountain National Park” by Jeff Connor, Joe Arnold, and Ken Czarnowski, 1992 George Wright Society Proceedings.


Ouzel Lake, Ouzel Creek
Bluebird Lake was fishless prior to the Bluebird Dam removal, and due to present barriers, it remains fishless. However, Ouzel Creek and Ouzel Lake, just downstream from Bluebird Lake, are important spawning habitat for greenback cutthroat trout (Oncorhynchus clarki stomias) one of three threatened salmonids native to Colorado east of the Continental Divide, and a few greenback cutthroat are also present upstream of the barrier above Ouzel Lake. Although repeated fish removal efforts occurred in the 1980s and 1990s to eliminate competing brook trout from the Ouzel Creek and Ouzel Lake area, annual electrofishing surveys by National Park biologists continue to observe an increase in brook trout and a serious decline in greenback cutthroat.  Park biologists plan to attempt other methods of brook trout eradication if greenback cutthroat populations continue to decline. For 1979 to 2000 gill net sampling and angler use data from Ouzel Lake and Ouzel Creek, click here.

Habitat surveys were conducted on the allopatric greenback cutthroat population of upper Ouzel Creek in 1997—a reach uncolonized by brook trout-- as part of a study to predict success of translocation based on habitat variables. Thirty-six fish were observed in pools in this one-kilometer section. A population status of “low” was assigned, and the habitat in upper Ouzel Creek was determined to have a 48.9 percent chance of becoming fishless, a 44.9 percent chance of supporting low numbers of cutthroat trout and a 7.1 percent chance of supporting high numbers of cutthroat trout. Habitat variables used to calculate these probabilities were as follows: 9.0 degrees Celsius mean daily July water temperature, 5.4 mean bankfull pool width, and 146 pools with a residual depth of less than 30 centimeters.   Recent surveys, however, indicate that the fish population in upper Ouzel Creek is indeed healthy and that recruitment is occurring.  Still-fishless Bluebird Lake is being assessed for suitability as a refuge for this population in times of potential stream dewatering, as it has suitable spawning substrate and an appropriate temperature regime.  There are some minor, but removable, barriers to access to the lake and spawning areas.

Pear Lake
In September 1988, following removal of the Pear Lake Dam, hybrid cutthroat trout were removed from Pear Lake and Cony Creek. Pear Lake was then stocked with greenback cutthroat, with a mean length of 161 millimeters, in June 1989, and with greenback cutthroat fry in 1989 and 1990. Cony Creek was stocked with fry from the outlet of Pear Lake to Calypso Cascades in 1989 and 1990. Based mostly on creel survey data and a 1998 gill net survey, it appeared that Pear Lake was populated by an abundance of fish. These fish were smaller than the hybrid cutthroat trout that were in the lake prior to the 1988 fish removal. In September 2000, a two-pass electrofishing survey was conducted at the Finch Lake Bridge on Cony Creek. The fish-per-100-meter figure was more than double what was estimated prior to the fish removal in 1988. For 1960s to 2000 gill net sampling and angler use data from Pear Lake, click here.

A habitat survey was conducted in 1996 on the lower section of Cony Creek from Calypso Cascades to Pear Creek. Twenty-two fish per kilometer were observed in pools throughout this section. In 1998 the section above Pear Creek was surveyed. Cony Creek above Calypso Cascades was rated a “high” population status, and was determined to have a 98.6 percent chance of supporting high numbers of cutthroat trout based on a stream-scale model for predicting translocation success. Habitat variables used to calculate these probabilities were as follows: 9.0 Celsius mean daily July water temperature, 5.4 mean bankfull pool width, and 146 pools with a residual depth of less than 30 centimeters.

For restoration purposes, the Pear Lake/Creek and Cony Creek greenback cutthroats are considered two separate populations, with a barrier between them.  According to 2001 and later creel surveys and observations, both populations are considered stable and self-sustaining as defined in the Greenback Cutthroat Trout Recovery Plan.

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(Before) Bluebird Lake Dam in 1989. Over the course of two summers, crews worke...
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Aerial view of the Pear Lake Dam site in 1989 after the dam was removed....
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Pear Lake Dam site 1993....

Sandbeach Lake
In September 1988, rainbow trout up to 500 millimeters in length, and a few longnose suckers, were removed with antimycin. In June 1989, Sandbeach Lake was stocked with greenback cutthroat 161 millimeters in mean length, and in September 1989 with greenback cutthroat fry.

Cutthroat were first observed spawning in the outlet in late June 1990. The reconstructed outlet stream is not completely sealed, and after spring flows subside, water flows above ground for about 30 meters before entering a small boulder field for a short distance. The best spawning substrate and juvenile rearing areas are present below this small boulder field. It is believed that this boulder field prohibits most fry from entering the lake. An abundance of fry is observed each fall below the boulders; however, the lake does not seem to support a large population of fish.

Due to the cold temperatures of the inlet, barriers to fish migration into the inlet, and low flows, spawning within the inlet stream above the lake is not possible. Fish have been observed trying to spawn at an alluvial fan in the lake at the inlet.

Catch rates for gill net surveys were high in 1989 and 1990 following the stockings in 1989. The 161-millimeter (mean length) fish stocked in June were found to be an average of 265 millimeters by September. Stomachs of fish sampled in 1990 were found to be full of chironomids, indicating an abundance of food present in the lake. Catch rates since 1990 have decreased significantly, with a low in 1998; meanwhile, mean, minimum and maximum lengths were increasing each time the lake was surveyed, indicating that there was not much recruitment occurring. During year-2000 hook-and-line surveys, however, fish as small as 176 millimeters were caught, indicating that some recruitment was taking place. Fish up to 407 millimeters were also caught. All fish that have been sampled were fat and in good health. In addition to gill net surveys conducted at the outlet trend site, surveys have been conducted near the inlet with very poor results. For 1960s to 2000 gill net sampling and angler use data from Sandbeach Lake, click here.

It appears, based on the available data, that the number of fish present in the lake is limited by the boulder field in the outlet which prohibits most fry from entering the lake after emergence. The fish that do enter the lake find an abundance of food, grow quickly and are fat and healthy. Although the number of fish in the lake is low, the biomass is believed to be high enough for the lake to be considered a stable, self-sustaining population as defined by the Greenback Cutthroat Trout Recovery Plan.

Sandbeach Creek
Although flows through Sandbeach Creek are low in the fall, two areas below the fish removal project were found to contain what looked to be good specimens of greenback cutthroat trout. Both areas were in beaver pond habitat, with one located above a steep canyon wall and the other located below the wall. At the time of the Sandbeach Lake fish removal, Sandbeach Creek was believed to contain a hybrid cutthroat/rainbow trout population.

Tissue samples were collected from both areas in 1999 and analyzed for genetic purity. The samples collected above the wall were determined to be A-greenback cutthroat with slight Yellowstone cutthroat influence from multiple sources. The fish below the wall were determined to be B+greenback cutthroat with a Yellowstone cutthroat influence from multiple sources. No influences from rainbow trout were detected at either location. It appears that pure greenback cutthroat trout fry that cannot enter the lake through the boulders at the outlet have been dropping out of Sandbeach Lake and mixing with the hybrids that originally were present.

In 2002, low snowfall in the park caused summer dewatering of some streams, including Sandbeach Creek.  One of the beaver-pond areas which previously held fish was no longer present.  However, fish were observed in pools below the dewatered area, and appeared to be actively feeding and showing no signs of stress.

Lawn Lake and the Roaring Fork River
The Lawn Lake population of greenback cutthroat has been longer-established, having been stocked in 1984 through 1986.  Following dam removal, surveys and observations indicated continued recruitment in Lawn Lake, as befits its status as a stable, self-sustaining population.  Suitable spawning areas exist at both the inlet and outlet to Lawn Lake; although restoration attempts were made in 2000 to improve the outlet area by removing barrier materials and buried pipe, the trout appear to be continuing their historical tendency to preferentially use the inlet for spawning. The Roaring River greenback cutthroats are considered a separate population for restoration purposes.  Estimates in 2004 and 2005 show a combined Roaring River population of nearly 4000 greenback cutthroat trout.  Although this is considered a stable and self-sustaining population, electrofishing surveys demonstrated that a significant number of the fish, up to 17 percent, showed signs of angling damage, particularly in the heavily-fished lowest 900 meters of the Roaring River.


Bighorn sheep continued to use the terrain above the lakes. The only negative wildlife impact documented was the noise of helicopters and heavy equipment and the constant presence of people, which caused ptarmigan to leave the area. Displacement of other wildlife from the direct vicinity of the lakes and dams occurred during demolition, but 1992 surveys document wildlife have returned to the area in close to pre-demolition numbers.


Based on late summer research conducted in 1988 by the Park's Plant Ecologist and Natural Resources Specialist, a decision was made in the spring of 1989 allowing mostly natural revegetation to occur. The lakeshores were recovering with a high diversity of native plants. Only one exotic plant colonized the dam sites of Sandbeach and Pear Lakes (Rumex aquaticus L. ssp occidentalis). Apparently this plant became established due to viable seed germinating from horse manure. Horses packed in food and other supplies to the work crews throughout the summer of 1988. Rumex was first observed where the horses were tied in 1988. By 1989 the plant was well-established throughout the dam sites of both lakes. Monitoring vegetation plots from 1989 to 1992 indicated that the rumex had reduced in density and percent cover, and was being replaced by natives. No exotics were found at Bluebird Lake. This also provided a unique opportunity to interpret and study natural succession of severely disturbed sites. Information about flora and fauna recovery at the lakes in Rocky Mountain National Park (RMNP) may be useful for other National Park Service Units if water reservoirs within their boundaries are restored. A plaque placed at the site of Bluebird Dam interpreted the monumental effort the National Park Service took to restore the area. This plaque was removed from the lakeshore in 2002, and a new plaque describing the removal of the dam was to be placed at the trailhead near the Wild Basin Ranger Station in 2005.

The shorelines around the lakes, except for the dam sites, have now been recovering since 1982. Surveys of vegetation along the shorelines first occurred at Lawn Lake in 1983 and at the other lakes in 1988 and 1989. By 1989 plant recovery along the lakeshores was well underway in most areas. Resource Managers established permanent vegetation plots at Sandbeach and Pear Lakes in 1989 and at Bluebird Lake in 1990. Vegetation plots were 10 x 15 meters in size with 10 plots randomly selected at Bluebird Lake, 16 at Pear Lake, and 10 at Sandbeach Lake. Percent vegetation cover varied along the lakeshores from 5 to 30 percent. Plant diversity was high along these lakeshores: 46 plant species were identified at Sandbeach Lake, 48 at Bluebird Lake, and 43 at Pear Lake. Only one exotic plant was found at Sandbeach and Pear Lakes. Percent vegetation cover was the lowest at Pear Lake (5 percent average) and the highest at Bluebird Lake (15 percent average). In addition, six smaller half-square-meter plots were established at Sandbeach, eight at Pear and seven at Bluebird Lakes. These plots were used for photo documentation, and analysis of plant succession and diversity. Photos of the plots were taken every year, and plant species were identified for the first five years and every three years thereafter. Measurements taken from the larger 10-by-15-meter plots were taken every other year for the first five years. Monitoring continued every year through 1993 and then every other year through 1998. By 2005, natural plant succession was indeed occurring on the lakeshore (verbal communication with Jeff Connor, RMNP Natural Resource Specialist).
Updated: August 9, 2007
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