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. 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 of dead storage in the reservoir (432,000 acre-feet), and the location of the dam’s outlet works. REPHRASE??

Kachess Reservoir FMO Habitat Overview

Kachess Lake was a glacially formed, natural lake but was elevated and is now managed as 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 communities include bull trout, kokanee, rainbow trout, cutthroat trout, pygmy whitefish, mountain whitefish, burbot, northern pikeminnow, speckled dace, sculpin, and redside shiner. 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 (KDRPP) to access the 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, pending studies that are looking into the potential impacts on the threatened populations of bull trout that reside there.

Habitat Monitoring

A limnological survey was conducted on Kachess Reservoir between 1998-2001 (Lieberman and Hiebert 2003). The authors reported 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" wheras 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 WA Department of Ecology in advanced 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 (20-22C) 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. 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.

ANYTHING I MISSED??

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. An antenna array is maintained directly downstream of Keechelus dam that has detected a single La Salle bull trout, presumably of Kachess River origin entrained at Kachess Dam (Beebe et al. 2025 a,b), however 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 five individual bull trout have been captured below Kachess dam, any loss of individuals to entrainment might impact the population. USFWS - HOW MANY CONFIRMED ENTRAINED KACHESS FISH (including captured at Keechelus???)

Dewatering due to flow management

Threat Severity: ____????

Kachess Reservoir FMO habitat does not dewater, but available habitat becomes limited and fish passage barriers may emerge in key migration corridors.

Land-use Issues

Forestry

Threat Severity: Unknown, likely insignificant

Water quality studies have shown Kachess Lake 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.

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.

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 and Box Canyon Creek and may be abundant in some of the tributaries, including Lodge Creek. The distribution in the watershed is unknown. Few brook trout have been observed in the Upper Kachess River. Hybridization has not been documented here. CONFIRM. 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 have not fully established 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 draw-down of Kachess Reservoir, such as under a KDRPP scenario, would have food web level impacts due to reduced littoral prey production (Hansen et al. 2017) and would likely impact bull trout habitat use and hunting behaviors (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 239,000 acre feet, there is significant volume of water remaining even under full-draw down conditions. However, some bull trout may be drawn south under drought conditions where there are fewer habitat limitations (Hamilton et. al 2025). This reduces spawning potential when there may be passage barriers 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

In Kachess Reservoir, fishing is legal and open year-round. Fishing is very common, especially in the summer and the target species is primarily kokanee. A WDFW creel survey in 2022 found no retained bull trout, but had 3 bull trout reported as "caught and released". Modeling expanded the predicted catch rate to ~28 bull trout per year. With an adult population of ~100 bull trout, 28 is nearly 30% of the population, caught and handled annually. 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. More research needs to be done to understand the impacts of angling to these populations.

Management/Monitoring (Research)

Threat Severity: Insignificant

USFWS - comment on how research activities may or may not be a threat.

Summary of Primary Limiting Factors and Threats

DISCUSS DURING WORKSHOP

Bull Trout Recovery Actions for Kachess FMO

DISCUSS

Monitoring Needs/Key Questions

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DISCUSS

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 XXXXXXXXXXXXX

Specific detail on out of cycle updates: