A. Ecosystem function

Core strategy

Protect and restore natural ecosystem functions, habitats, and biological diversity wherever feasible consistent with biological objectives in the program.


Restoring functioning ecosystems in fish and wildlife habitat is critical to the long-term success of measures supported by this program to mitigate the impacts of hydropower dams in the Columbia River Basin. The extent to which these can be restored is constrained by the reality that the hydroelectric system will continue to provide essential services to people in the Pacific Northwest, and that passage improvements at the dams alone are not likely to fully mitigate these impacts. Recognizing this reality, the Act authorizes “offsite mitigation,” areas outside of the immediate area of the hydrosystem — in the tributaries and subbasins off the mainstem of the Columbia and Snake rivers, and in the lower Columbia River and estuary. Implementing offsite mitigation provides the greatest opportunities for habitat improvements as a means of offsetting some of the impacts of the hydrosystem. This off-site mitigation does not reduce the need to mitigate in the mainstem of the Columbia and Snake rivers as, historically, these were among the most productive spawning and rearing habitats for salmonids and provided essential resting and feeding habitat for mainstem resident and migrating fish. Thus protection and restoration of mainstem habitat conditions, and offsite mitigation, are critical pieces of this habitat-based program. The program mitigates for hydropower system impacts by restoring ecosystem functions in these habitats in conjunction with passage improvements at the dams.

Guidance on specific habitat mitigation activities are in subbasin plans, which have been developed for most of the subbasins and the mainstem reaches in the Columbia River Basin. These plans include assessments of current physical and biological conditions and also identify factors that limit the productivity and capacity of focal species in priority reaches.


  • Ecosystem function, which means the ability of a river to sustain healthy populations of fish, wildlife, and plants, is enhanced by environmental conditions that support healthy populations.
  • The existence of hydropower dams can reduce or degrade ecosystem function by impounding reservoirs, trapping or containing pollutants, raising water temperatures, disconnecting floodplain habitats, providing habitat for non-native invasive species and native and non-native predators, and through other related impacts.
  • An adaptive and flexible suite of river and dam operations that can respond to changing environmental conditions, from flow fluctuations to climate-change impacts, can help improve degraded ecosystem function.
  • Ecosystem function can be improved in the Columbia and Snake river tributaries by, for example, repairing and restoring riparian habitat in spawning areas, restoring native vegetation, and changing land-management practices that can degrade water and habitat quality.

General measures

  • Identify and protect mainstem habitat areas and ecological functions that are relatively productive for spawning, resting, rearing, and migrating native anadromous and resident focal fish species and manage these areas to protect aquatic conditions and form a transition to floodplain terrestrial areas and side channels.
  • Restore and enhance habitat areas that connect to productive areas to support expansion of productive populations and to connect weaker and stronger populations so as to restore more natural population structures.
  • Protect, enhance, restore, and connect freshwater habitat in the mainstem and tributaries.
  • Protect and enhance ecological connectivity between aquatic areas, riparian zones, floodplains, side channels, and uplands.
  • Where feasible, reconnect protected and enhanced tributary habitats, especially in areas with productive populations.
  • Identify, protect, enhance, and restore the functions of alluvial river reaches.
  • Allow for biological diversity and complexity to increase among and within populations and species to increase ecological resilience to environmental variability and allow for greater life history and species diversity.
  • Manage water to provide appropriately timed streamflows that promote productive populations of anadromous fish and resident fish. Where feasible, support seasonal fluctuations in flow and quantity, while reducing large, rapid, short-term fluctuations. Ensure that any changes in water management are premised upon and proportionate to scientifically demonstrated fish and wildlife benefits.
  • Frame habitat restoration in the context of measured trends in water quantity and quality.
  • Decrease the disparity between water temperatures and the naturally occurring regimes of temperatures throughout the basin, using stored water to the extent feasible to manage water temperatures downstream from storage reservoirs where temperature benefits from releases can be shown to provide improved fish survival.
  • Identify, protect, enhance, restore, and connect ecosystem functions in the Columbia River estuary and near-shore ocean discharge plume as affected by actions within the Columbia River mainstem.
  • Evaluate flow regulation and changes to estuary-area habitat and biological diversity to better understand the relationship between estuary ecology and near-shore plume characteristics and the productivity, abundance, and diversity of salmon and steelhead populations.
  • Understand the status of the Columbia River ecosystem in terms of habitat and other ecosystem features (both natural and human-caused) to better inform Council decisions.
  • Develop metrics of juvenile recruits-per-spawner in order to evaluate habitat effectiveness.

The following eleven strategies are sub-strategies of the overarching ecosystem function component of the program.

← IV. Strategies — how the program will achieve the changes

1. Habitat →

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