Kachess Reservoir FMO Habitat

Kachess Reservoir Adfluvial Populations

Kachess Lake was a natural lake prior to the construction of Kachess Dam on its outlet in 1912. At full pool the lake holds 239,000 acre-feet of water with a surface area of 4535 acres. The dam is a complete barrier to migration, isolating two local populations of bull trout, which now reside in the lake and spawn in upstream tributaries. One spawns in Box Canyon Creek and the other, in the upper Kachess River. Both of these populations are relatively small with each having a limited amount of spawning and rearing habitat available below waterfalls that block further upstream access. Several other smaller tributaries also flow into Kachess Lake. None are known to support bull trout spawning, but some support bull trout FMO habitat. See Kachess Lake Bull Trout Population Group page for more details on population genetics and monitoring.

As is the case for the other adfluvial populations in the Yakima Basin, the potential exists for individuals to be entrained through the unscreened outlet works of the dam and permanently displaced downstream. The likelihood of this occurring is reduced because the large amount of inactive pool in the reservoir (585,000 acre feet) provides habitat refuge even when the reservoir is drawn down.

Kachess Reservoir FMO Habitat Overview

Kachess Lake was a glacially formed, natural lake but its maximum elevation was increased and is now managed as a reservoir since the construction of Kachess Dam in 1912. Kachess is larger than Keechelus in both volume and surface area (Hansen et. al 2017). It is an oligotrophic lake, with the food web consisting of benthic and pelagic fishes, macrozooplankton, and benthic invertebrates. The fish community includes bull trout, kokanee, rainbow trout, cutthroat trout, pygmy whitefish, mountain whitefish, burbot, northern pikeminnow, speckled dace, sculpin, redside shiner, and Eastern brook trout in small numbers. The reservoir is 430 ft (130m) at its deepest point, which offers year-round temperature refuge for cold water species, like bull trout. The name Kachess comes from a Native American term meaning "more fish", in contrast to Keechelus Lake whose name means "few fish" (Phillips 1971).

The reservoir is used for water storage to support a multi-billion dollar agricultural industry downstream in the Kittitas and Yakima valleys. There is a proposed action to design, construct, fund, operate and maintain a floating pumping plant, the Kachess Drought Relief Pumping Plant (KDRPP) to access an additional 200,000 acre-feet of water that are inaccessible with the current configuration of the dam's outlet works (USBR and Ecology 2015). Currently, only 239,000 acre feet are able to be withdrawn. The project has been on hold due to the high cost and the implications for the structures impact on spring flows. Additionally, the project will not move forward until studies that are looking into the structure's potential effects on the threatened populations of bull trout are complete.

Neither the sparse shoreline development or water sports activities on the lake are believed to influence habitat quality. The effects of reservoir depletion during the summer and early fall are less concerning in Kachess Reservoir than in any of the other Yakima basin impoundments for a few reasons. 1) The reservoir has a conservation pool (i.e., inactive storage) of 585,000 acre-feet that cannot be accessed for irrigation withdrawal. 2) Reservoir depletion doesn't occur until late in the season (August through September) due to the release schedule that prioritizes Keechelus, then Cle Elum, then Kachess Reservoirs. However, in drought years when the reservoir is drafted to its lowest level, the Kachess Narrows may inhibit or discourage passage between Big and Little Kachess due to the elevated water temperatures and lack of habitat cover (Taylor 2022). Under a KDRPP (Kachess Drought Relief Pumping Plant) scenario, the Kachess Narrows could completely block upstream passage for up to five years depending on weather conditions. Under this condition, some bull trout would not be able to access their spawning grounds. Even under current operations, back to back drought years can limit reservoir refill and create thermal barriers at the Kachess Narrows (Hamilton et al. 2025).

Habitat Monitoring

Mongillo (1982) measured water quality parameters and zooplankton densities in Kachess Reservoir.

A limnological survey was conducted on Kachess Reservoir between 1998-2001 (Lieberman and Hiebert 2003). The authors studied refill ratio (0.9:1) and flushing rates (~95 - 282 days) as well as temperature conditions, turnover timing, and other water quality parameters like pH and dissolved oxygen. The study concluded that nutrient concentrations were very low, but samples were only collected in the top 10m of the water column. Water clarity was measured by Secchi disk. Kachess had the highest visibility over all of the other Yakima Basin reservoirs, reflecting a negligible concentration of chlorophyll a. Based on chlorophyll a concentrations at the time, Kachess would have been classified as "ultraoligotrophic" whereas Bumping, Cle Elum and Keechelus were classified as "oligotrophic" (Lieberman and Hiebert 2003). The authors also reported the dominant species of phytoplankton and zooplankton

USFWS reported on hydrological conditions in Kachess Reservoir from 2001-2008 (Thomas 2007). His primary conclusion was that reservoir drawdown actions are the most consistent indicator of poor passage conditions at Box Canyon Creek between 2001-2006.

WDFW was tasked with providing fish, wildlife and habitat data to the WA Department of Ecology in advance of the Environmental Impact Statement for KDRPP and Kachess to Keechelus conveyance (WDFW 2015). Results can be found in the referenced report.

There was a study done on food web interactions in Kachess and Keechelus reservoirs, which looked at 1) food web structure, 2) foraging and growth environment for bull trout and kokanee and 3) consumption demand vs. food supply for key predators and prey (Hansen et al. 2017). 1) Results showed that the Kachess Reservoir food web is supported by more benthic and littoral production compared with Keechelus lake (pelagic). The primary forage base for bull trout was found to be pelagic oriented fish like kokanee and other salmonids. Kokanee were listed as a significant prey source for bull trout, which themselves primarily fed on Daphnia, when available. 2) Measurable thermal stratification occurs in the summer, peaking in July and breaking down in October. Epilimnetic temperatures (20-22°C) can significantly reduce growth potential of kokanee and bull trout. Daphnia concentration peaked in April-June in Kachess and the organisms concentration was highest in the epilimnion, potentially limiting access by predators due to temperature limitations. Mature kokanee were found to be vulnerable to predation by burbot and pikeminnow during their pre-spawn period. This time period is also when bull trout are nearshore, increasing potential competition. 3) Feeding rates of bull trout (estimated from a bioenergetics model) are not limited by foraging opportunities under contemporary conditions (annual stocking of ~365,000 kokanee) and the kokanee population could support a larger number of bull trout in the reservoir (Hansen et. al 2017).

USFWS conducted a study at Kachess Reservoir between 2022-2023 that detailed the implications for bull trout distribution and fish passage under drought conditions and reservoir drawdown (Hamilton et. al 2025). They concluded that bull trout distribution was impacted in a drought year, and that distribution shifted south, to "Big Kachess" where there was more lentic habitat available. There were no movements across the Kachess Narrows into "Little Kachess" after July 2023, indicating a barrier to movement and reduced spawning potential. This was not true in 2022, a non drought year.

Entrainment

In 2011, the USBR conducted an entrainment study directly below Kachess Dam. A screw trap and a fyke net were deployed in the river channel to capture fish entrained through the outlet works of the dam and passed to the river below. The sampling was done over a range of flow releases from mid-June through mid-October. Nearly 2,700 fish were captured during the course of the study representing 16 species, but no bull trout were collected (Arden Thomas, USBR, pers comm). However, the USFWS has encountered five entrained Bull Trout below Kachess Dam since 2022: three rescue and rear fish presumably from the Kachess River, one untagged fish of Kachess River origin, and one Gold Creek-origin fish entrained at Keechelus Dam. A single Box Canyon Creek origin bull trout has been collected at the base of Keechelus Dam (Haskell et al. 2022). An antenna array is now maintained directly downstream of Keechelus dam that has since detected a single La Salle bull trout, presumably of Kachess River origin entrained at Kachess Dam (Beebe et al. 2025 a,b). A similar antenna below Kachess Dam in the lower Kachess River is needed.

Threats

Connectivity

Fish Passage Barriers

Threat Severity: Significant

Kachess Dam is a complete passage barrier to upstream migration. The Kachess Narrows have also proved to limit fish passage in drought years (Hamilton et. al 2025).

Entrainment

Threat Severity: Unknown, likely significant

Although only four individual bull trout with genetic origin from the upper Kachess River have been encountered below Kachess dam, any loss of individuals to entrainment might impact the population. There is a distinct lack of tagged fish from the Box Canyon Creek population, making entrainment studies difficult.

Dewatering due to flow management

Threat Severity: Insignificant

Kachess Reservoir FMO habitat does not dewater, but dewatering in key migration corridors (Kachess Narrows, mouths of Box Canyon Creek and the upper Kachess River) do occur at low pool elevations.

Land-use Issues

Forestry

Threat Severity: Unknown, likely insignificant

Water quality studies have shown Kachess Reservoir to have the highest clarity and most nutrient-poor water in the YRB (Lieberman and Hiebert 2003). This indicates forestry practices (current and historic) are not impacting water quality. One concern is the lack of forest thinning and ladder fuel reduction, which may result in a catastrophic wildfire, potentially threatening Kachess FMO habitat.

Agriculture and Grazing

Threat Severity: Insignificant

There are no agriculture or grazing threats to Kachess FMO habitat.

Recreation

Threat Severity: Unknown

The majority of recreational impacts probably occur on the West side of the reservoir in and around Kachess Campground. The campground has ~100 developed campsites and stays busy throughout the summer season. There is a motorized and a non-motorized boat launch, so water activities are popular including fishing, boating, kayaking, stand up paddle boarding and swimming. There has been a substantial increase in outdoor recreation since 2020, with people new to the activity not knowing best practices like "Leave no Trace." Impacts are unquantified but downstream effects of trash, human feces, etc. may impact water quality.

The East side of the reservoir has an unpaved USFS road (4818) that also allows access to the Southern side of the reservoir. There are several access points and dispersed camping areas (i.e. "Freeloader Beach"). The USFS has observed an increase in resource damage and garbage, etc. on this side of the reservoir.

Roads and Development

Threat Severity: Insignificant

There are approximately 5 miles of road along the West shore of Kachess Reservoir to allow access to housing developments and the campground. This road is not thought to have negative population effects. Housing and the campground are probably not impacting bull trout negatively.

The East side of the reservoir has an unpaved USFS road (4818) that also allows access to the Southern side of the reservoir. There are several access points and dispersed camping areas

Mining

Threat Severity: Insignificant

Copper mining occurred in the upper Mineral Creek watershed but there is no current threat from mining to Kachess FMO habitat.

Ecological Interactions

Brook Trout

Threat Severity: Unknown, likely insignificant

Brook trout have been observed in Kachess Reservoir, Box Canyon Creek and the upper Kachess River and may be abundant in some of the tributaries, including Lodge Creek. The distribution in the watershed is not fully understood but two different surveys indicated that they are abundant in Lodge Creek (Scott Kline, WDFW, personal communication). A one-night survey of Thetis Creek and Gale Creek in 2014 suggest that brook trout are not in Gale Creek, but one char was seen in Thetis Creek (unknown whether bull trout or brook trout). An electrofishing survey in the unnamed tributary on the northwest side of the reservoir found zero fish. Only six brook trout have been observed in the upper Kachess River during demographic surveys, and seven brook trout in Box Canyon Creek. Hybridization has not been documented in either population of bull trout. When brook trout are observed during demographic surveys in Box Canyon Creek, snorkelers attempt to capture and cull the fish. Kachess Reservoir tributaries may be a good candidate for brook trout suppression and/or eradication because they do not appear to be abundant in bull trout spawning and rearing tributaries.

Other Invasive Species

Threat Severity: Insignificant

There are no other invasive species impacting Kachess Reservoir FMO habitat.

Diminished Prey Base

Threat Severity: Insignificant

A 2017 study in Kachess Reservoir found that feeding rates of bull trout are not limited by foraging opportunities and that the prey base in the reservoir could support larger populations of bull trout (Hansen et al. 2017). The authors noted that annual stockings of kokanee are an important source of prey for bull trout in Kachess and should continue. These stocked kokanee probably make up for the lack of anadromous smolt production after the construction of Kachess Dam.

Extensive drawdown of Kachess Reservoir, such as under a KDRPP scenario, would reduce littoral prey production and lead to food-web compression (Hansen et al. 2017), resulting in reduced foraging efficiency and shifts in bull trout habitat use and prey selection (Taylor 2022).

Disease

Threat Severity: Insignificant

No instances of disease have been reported.

Water Quantity and Quality

Flow issues/dewatering

Threat Severity: Insignificant

With a conservation pool of around 585,000 acre feet, there is significant volume of water remaining even under full-draw down conditions. However, some bull trout may be drawn to the "Big Kachess" basin under drought conditions where there are fewer habitat limitations (Hamilton et. al 2025). This reduces spawning potential when there are potential passage barriers (thermal or lack of water) at The Narrows.

Current and modeled future temperature conditions

Threat Severity: Unknown

Despite adequate depth refuge from unfavorable surface water temperatures, the onset of thermal stratification may be sooner and extend longer under warmer and dryer climate conditions. This may cause changes in predator-prey dynamics and migration abilities to the spawning grounds.

Fisheries Impacts

Angling Regulations/Fisheries Use/Poaching (Recreational)

Threat Severity: Unknown, likely significant

Fishing is popular in Kachess Reservoir, but the target species is primarily kokanee. A WDFW creel survey at Kachess Reservoir in 2022 observed no harvested bull trout throughout the busy summer season (Divens 2026). However, three bull trout were reported caught and released by anglers, which equated to an estimated 28 in total. An additional 11 fish were reported caught, unidentified and released, some of which were possibly bull trout. It is likely that some portion of the bull trout caught and released by anglers succumbed to hooking mortality. Low reservoir population numbers may limit the number of bull trout encountered by anglers. Angler education on bull trout identification and angling regulations seems to help reduce the number of bull trout lost to recreational angling (Divens 2026). While the exact impact of fishing/poaching is unknown, it is not zero. With the population trend for Kachess River and Box Canyon Creek bull trout, any level of catch or harassment could have significant negative impacts.

Additionally, many BTWG members have personal experience and observation that indicates illegal fishing may occur near staging areas (mouth of Box Canyon and Kachess Rivers) and at night, when bull trout are more active. However, it is anecdotal and not well documented. More research needs to be done to understand the impacts of angling to these populations.

Management/Monitoring (Research)

Threat Severity: Insignificant

Research in Kachess Reservoir FMO habitat was limited to an acoustic telemetry study between 2020-2023. Acoustic receivers were placed within the reservoir to detect sound signals from individual tags. Receivers were visited via boat and removed upon the end of the study when tag batteries were dead.

Summary of Primary Limiting Factors and Threats

The primary threats facing bull trout in Kachess Reservoir FMO habitat are related to lack of volitional fish passage at Kachess Dam, entrainment through the dam, and potential passage issues at the Kachess Narrows.

Bull Trout Recovery Actions for Kachess FMO

Kachess FMO Action #1: Provide connectivity at Kachess Dam

Kachess FMO Action #2: Assess and address the passage issues at the Kachess Narrows

Kachess FMO Action #3: Limit entrainment at Kachess Dam

Monitoring Needs/Key Questions

Ongoing research at the Kachess Narrows to understand:

A) factors influencing movement (i.e. temperature, physical habitat, food availability, etc.).

B) general fish passage conditions between August and October.

Update Notes

2012 BTAP text copied into Yakipedia and edited to match new format in November 2025 by Aimee Taylor. ADD LINK TO 2012 BTAP pdf placemark

Additional edits proposed by Alex Conley, Aimee Taylor and Kachess Populations small group. Reviewed, and updated and approved by BTWG in February 2026.

Specific detail on out of cycle updates: