Lower Columbia River Mainstem

The Columbia Gorge Subbasin Plan concerns the mainstem Columbia River between Bonneville and The Dalles dams in western Oregon and Washington. Tributaries to this reach, Bonneville Reservoir, are included in other subbasin plans, thus are not included here. The Oregon Department of Fish and Wildlife (ODFW) is the designated lead entity for developing the plan. ODFW is a co-manager of the fish and wildlife resources of the subbasin. ODFW’s mission is to protect and enhance Oregon’s fish and wildlife and their habitats for use and enjoyment by present and future generations. The planning process involved a number of federal, tribal, state, and local agencies, as well as regional organizations.


Subbasin Overview

Bonneville Reservoir includes the present wetted channel from the forebay of Bonneville Lock and Dam upstream through the tailrace of The Dalles Dam. It includes the embayments, backwaters, and mouths or lower reaches of tributaries and associated seasonally flooded and riparian lands. Bonneville Dam impounded the Columbia River at river mile 145 in 1938. The Dalles Dam was built in 1957 at river mile 191. Bonneville Reservoir is entirely within the Columbia River Gorge National Scenic Area.

The drainage area of the subbasin and its tributaries is about 3,300 miles2 (8,500 km2), approximately 1.4 percent of the entire Columbia River Basin upstream of Bonneville Dam. The volume of the reservoir is 537 kaf and average. Tributaries of the subbasin contribute approximately 3.9% of the discharge through the subbasin.

Landscape surrounding Bonneville Reservoir is characterized by steep forested hillsides underlain by basalt up to 1,524 m thick with sedimentary and recent alluvium deposits. Elevations range from about 53 m below mean sea level (the deepest river bed elevation in Bonneville Reservoir) to over 1,150 m on mountains bordering the river just west of Hood River, Oregon. The valley floor is naturally and artificially constrained to various extents throughout the subbasin depending on the slope at and above the shores.

The combined effect of climate, soils, and geology on terrestrial habitat types is manifest in the types of plant communities present along the edges of the subbasin and on its islands. Historically, the western third of the subbasin was forested with conifers and hardwoods with smaller areas of riparian wetlands. The approximate middle third of the subbasin transitioned from coniferous forest with ponderosa pines to dominant ponderosa pine forest. The eastern- most third of the subbasin changed to grasslands and then to shrub steppe habitat to the east.

Modern land uses within the subbasin include residential, commercial, and industrial development in urban centers including Stevenson, Home Valley, and Bingen, Washington and Cascade Locks, Hood River, and The Dalles in Oregon. The three Oregon urban centers contain marine industrial sites of varying sizes consisting of maintained harbors, reclaimed building sites, and shoreline moorings. Highway S.R. 14 parallels the north shore throughout the subbasin and Interstate Highway 84 runs along the south shore. The Burlington Northern Railroad runs parallel to the north shore and the Union Pacific Railroad runs along the south shore. These transportation corridors are reinforced by riprap revetments along significant lengths of shoreline. Hydraulic connection beneath portions of the transportation corridor between embayments (and mouths of streams) and the river’s mainstem is accomplished through culverts, bridges, and trestles. Agriculture is prominent along the middle and eastern portions of the subbasin, particularly on the southern side of the river. State and federal land ownership along the shoreline throughout the subbasin (including islands) is extensive.

Bonneville Reservoir was developed and is operated by the U.S. Army Corps of Engineers for hydropower generation and navigation. Other river uses include recreation (e.g., angling, windsurfing, kite skiing, boating, water skiing, sightseeing, bird watching, swimming, and waterfowl hunting) and tribal commercial, ceremonial, and subsistence fishing.

Islands are a significant component of Bonneville Reservoir particularly for birds and other wildlife. They provide important protection to many species from disturbance and predation, provide nesting habitat for a number of bird species, and could represent a potential dispersal route between reservoir shores. Islands are distributed throughout the reservoir.

The largest island in the reservoir is Wells Island, downstream from the mouth of Hood River. Prior to construction of Bonneville Dam, it was connected with the mainland and had a land area over twice as large as the 50 acres that remain uninnundated. Portions of its shoreline are actively eroding, threatening existing wildlife habitat. The island is the site of the only blue heron rookery in Bonneville Reservoir (the rookery has not been inhabited in recent years). It has some of the last remaining hardwood habitat of its type in the reservoir, and has potential to fill nesting requirements of important bird species like the bald eagle (personal communication, C. Flick, USFS, Hood River). Invasive plants including Himalayan blackberries, scotch broom, and thistle has begun to encroach. The island is owned and managed by USFS.

Fish Species Characterization and Status

A diverse community of fishes exists during at least some life stage in the subbasin. Thirtyseven species in 13 families have been observed. Of these, 17 species in six families are exotic or non- native. The eulachon and chum salmon have been extirpated from the subbasin since development of the federal Columbia River power system. Most of the species observed remain in the subbasin throughout their life naturally or because they are largely constrained within the barriers presented by Bonneville and The Dalles dams (e.g., white sturgeon). Anadromous fish that primarily use the subbasin as a migration corridor (upstream as adults and downstream as juveniles) include stream-type Chinook and sockeye salmon. Species that may use the subbasin for significant portions of their life history include Pacific lamprey, American shad, bull trout, ocean-type Chinook salmon, coho salmon, and rainbow trout (steelhead).

Selection of Focal Fish Species

White sturgeon fisheries are intensively managed, and the majority of harvest upstream of Bonneville Dam occurs in Bonneville Reservoir. The animal uses the benthic environment extensively, is long-lived, and matures at comparatively older ages. Its diet is unique compared to other fishes and includes benthic invertebrates, some of which are long-lived bio accumlators (e.g. alien and native mussels). The sturgeon is assumed to be an important indicator of sediment quality. They are largely confined within the reservoir and subject to the environmental conditions unique to that reservoir. The fish is significant to tribal culture. Availability of stock assessment information is considerable.

Chum salmon are listed under federal ESA, historically entered the planning area, and are genetically similar to chum salmon in the Bonneville Dam tailrace. Their historic range may contribute importantly to the species’ spatial structure and diversity. They spawn in low gradient streams or seeps that may have been inundated or affected by reservoir operations. Juveniles have a different vulnerabililty to environmental stressors than other salmonid species, because of their relative small size at outmigration.

Pacific lamprey are a state species of concern and have been petitioned to be listed under the federal ESA. They have unique adult upstream passage requirements and a prolonged juvenile rearing period in fine substrates. The portion of their life history spent within Bonneville Reservoir is uncertain, but adults are known to stage for a prolonged period, and larvae and ammocoetes have been known to occur in large mainstem river systems. Both adults and juveniles are prey for mammals, birds, and fish. They are significant to tribal culture.

Wildlife Species Characterization and Status

Because information on population dynamics is often lacking or less detailed for non-game wildlife compared to fish species, this assessment is less detailed. This assessment attempts to use the NPPC-sponsored Interactive Biodiversity Information System (IBIS) to characterize wildlife habitat types and long term changes at a broad scale. Also, because the numbers of species are large, the scope of the assessment is narrowed by identifying focal species that rely on habitats that are unique to Bonneville Reservoir, and depend on both aquatic and terrestrial habitats. Inventorying habitat structure or quantifying “key ecological functions” is beyond the scope of this draft subbasin plan. However, these principals are discussed briefly using Wells Island as an example.

Selection of Focal Wildlife Species

Bald eagles nest, forage, and overwinter in the Columbia Gorge Ecoprovince. They are listed under state and federal ESAs and are of national cultural significance. They have a direct link to aquatic resources (e.g., they prey on fish and waterfowl). They have an important ecological role by contributing marine nutrients to uplands. They can be an important indicator of forest structure (availability of large trees for nest sites and roosts) and water quality (they are relatively long-lived and susceptible to contaminants accumulated in their prey).

The western pond turtle is declining throughout most of its range, is highly vulnerable to extirpation in Oregon and Washington, and has been extirpated from most of its range already. As a result, the western pond turtle has been listed as endangered by the state of Washington.

Three populations remain in the Columbia River Gorge, two in Washington and one in Oregon. The total number of western pond turtles in known Washington populations is estimated at only 250-350 individuals, many of which went through the head-start program at the Woodland Park and Oregon zoos. Additional turtles may still occur in wetlands that have not been surveyed. The species requires a continued recovery program to ensure its survival until sources of excessive mortality can be reduced or eliminated.

Limiting Factors and Conditions

White Sturgeon

Recruitment to the population is thought to be the key factor controlling the abundance and population structure of white sturgeon. Therefore, we list recruitment to the egg/larval stages as a primary limiting factor for all life stages. Impacts of predation on white sturgeon at various life stages are poorly understood, as are ecological interactions between sturgeon of various life stages and other species, making it difficult to identify limiting factors in these areas. Connectivity and passage issues are likely limiting factors for nearly all life stages of white sturgeon. The impacts of contaminants on white sturgeon populations are relatively poorly understood. Negative impacts may include reduced spawning success and reduced growth, as well as direct or delayed mortality. Harvest by sport and commercial fisheries are limiting factors for all life stages to the extent that they impact the available abundance of spawning size fish, which produce subsequent generations.

Chum Salmon

Factors that limit production of chum salmon in the Columbia River Gorge are not explicitly known. Assuming that historical populations of chum salmon upstream of Bonneville Dam experienced the same stressors in the lower river, estuary, and ocean, as the populations downstream of Bonneville Dam, factors that could limit chum salmon production in the Columbia River Gorge include: 1) Loss of habitat through inundation by Bonneville Dam; 2) Lower propensity to ascend the fishways at Bonneville Dam compared to other anadromous species; 3) Blockage to tributary habitats created by the transportation corridors or hatchery weirs; 4) Sedimentation of spawning and rearing habitats in tributaries and nearshore areas of the mainstem; 5) Intermittent dewatering of spawning gravels caused by operation of the FCRPS; 6) Land use development along low gradient streams; 7) Decreased rate of recruitment of large woody debris to lower reaches of tributaries and nearshore areas of the mainstem; 8) Changes to seasonal and longer term recruitment of coarse sediments (spawning gravels) from operation of the FCRPS and tributary dams (Condit and Powerdale dams).

Pacific Lamprey

Without better knowledge of the distribution and duration of residency at different life stages, describing explicit factors in Bonneville Reservoir that limit the production of Pacific lamprey is difficult. Out-of-basin factors impacting Pacific lamprey are present at Bonneville and The Dalles dams, where passage measures developed for salmonids do not necessarily provide optimum benefits to migrating juvenile and adult lampreys.

If adults overwinter in the reservoir, holding conditions are assumed to be adequate in terms of availability of boulder habitat, and water temperature and quality. The availability of fine sediments is extensive in the reservoir. However, the frequent pool elevation fluctuations are likely to negatively impact the ability of juveniles to use nearshore substrates for sustained periods. Juveniles are likely to be susceptible to contaminants because they rear in fine substrates for prolonged periods. Catastrophic events such as chemical spills have the potential to impact lampreys more greatly than other fishes, because multiple year classes coexist in freshwater habitats, and die offs can contribute greatly to population instability.

Bald Eagle

Generally, factors that can limit production of bald eagles include human-related killing, poisoning, habitat destruction and alteration, changes to prey base, and disturbance by humans. Based on the fact that the number of bald eagles appears to be increasing in the Columbia Gorge subbasin, working hypotheses (assumptions) used to suggest potential limiting factors include: 1) Contaminants in fish and waterfowl eaten by bald eagles appear to be low enough so reproductive potential of mature birds persists; 2) Purposeful (illegal) killing of birds if it still exists, is presently low enough so survivorship of mature birds is adequate to sustain existing population levels in the Columbia Gorge subbasin; 3) Availability of forage appears to be adequate to sustain existing population levels in the Columbia Gorge subbasin; 4) Availability of perching, roosting, and nesting sites appears to be adequate to support existing population levels; 5) Perching, roosting, and nesting habitat closest to water (including islands) represents optimum habitat.

Western Pond Turtle

The western pond turtle has a long life span, requires 10 or more years to reach reproductive age, and has a low rate of recruitment. The vagaries of Pacific Northwest weather probably result in high variation in hatching success. The combination of these factors makes this species especially sensitive to any increase in chronic sources of mortality or other factors that affect reproduction and recruitment.

Human population increases and concomitant development will continue to alter or eliminate habitat for nesting, increase the rate of predation on nesting females, nests, or hatchlings, and/or expose hatchlings to hazardous post-hatching conditions. Alteration of aquatic habitats, by water diversion projects or similar situations, may impose considerable hazard and hardship on moving turtles and result in higher than normal levels of mortality.

Introduced species have changed the ecological environment in the region for pond turtles. As significant predators on hatchling and small juvenile western pond turtles, non-native species such as bullfrogs and warm water fish seem to reduce survivorship and alter recruitment patterns.

The western pond turtle appears to be relatively sensitive to disturbance. Disturbance may affect the frequency and duration of basking or foraging behavior, which may be particularly important for gravid females. Interruption of basking may lead to a delay in the maturation and deposition of eggs, leading to a decrease in hatching success or overwinter survival. Boat traffic and fishing may influence western pond turtle behavior or cause direct mortality.

Management Plan

The management plan builds on information in the assessment and inventory, expresses the subbasin vision, and proposes biological objectives, strategies, and research, monitoring, and evaluation needs.


“An ecosystem with productive and sustainable levels of fish and wildlife that provide substantial and sustainable environmental, cultural, recreational, and economic benefits”

Stakeholders representing local, state, and federal entities in the Oregon portion of the lower Columbia River Gorge crafted the vision for the management of fish and wildlife and their habitats.

Biological Objectives and Strategies

Biological objectives based on the vision statement were developed for each focal species. Objectives explain how limiting factors will be addressed and describe the resulting changes in biological performance of the focal species. Strategies are directly linked to achieving biological objectives. Strategies are prioritized as follows:

Urgent needs: These strategies must be continued or implemented as soon as possible to achieve objectives and/or curtail losses.

High priority needs: These are part of a longer view to achieve objectives, but failure to continue or medium-term delays in implementation will not result in immediate or irrecoverable losses.

Information needed: These strategies may have strong merit in particular circumstances, but the benefits and risks need to be investigated to understand details of implementation or potential conflicts with other objectives or strategies.

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