Key Limiting Factor |
Impairment |
Habitat Affected |
Threat Type |
Threat Name |
Life Stage (s) |
Description |
Habitat Quantity and Quality |
Access and Availability; Morphological Changes |
Estuary |
Agricultural Practices; Urbanization |
Diking; Filling; Riparian Degradation; Wetland Loss |
Smolts |
Historical complex habitats have been modified through channelization, diking, development and other practices. |
Habitat Quantity and Quality |
Morphological Changes |
Freshwater-Floodplain |
Agricultural Practices; Urbanization |
Diking; Impervious Surfaces (Road Density); Riparian Degradation; Wetland Loss |
Juveniles |
In areas modified through riprapped banks, dredging, and elimination of off-channel refugia the diversity of overwintering habitat has been reduced or eliminated. |
Habitat Quantity and Quality |
Small-Scale Structural Complexity; Morphological Changes |
Freshwater-Riparian |
Agricultural Practices |
Diking; Filling; Riparian Degradation |
Juveniles |
Cultivation, farming, and pasturing have reduced riparian habitat in many tributaries. Poor riparian condition throughout the subbasin limits Chinook productivity. |
Habitat Quantity and Quality |
Small-Scale Structural Complexity; Morphological Changes |
Freshwater-Instream |
Agricultural Practices; Forest Management |
Diking; Filling; Wood/Structure Removal |
All |
Pre-spawning Chinook are impacted by losses of habitat diversity and streambed instability in the middle and lower reaches of the Imnaha. Insufficient substrate size in the Middle and Upper Imnaha limits Chinook spawning and incubation success. |
Instantaneous Mortality |
Anthropogenic Mortality |
-- |
Fishery Management |
Harvest |
Adults |
Spring Chinook are primarily subject to freshwater harvest. |
Instantaneous Mortality |
Anthropogenic Mortality |
-- |
Dam or Hydropower Facility Management |
Migration Impediments |
Juveniles |
Juveniles and adults must pass eight mainstem dams during migration. |
Water Quality |
Turbidity; Temperature |
-- |
Agricultural Practices; Forest Management |
Diking; Filling; Riparian Degradation; Bank Destabilization |
Eggs, juveniles |
High temperatures affect the productivity of spring/summer Chinook in the Lower Imnaha. Summer temperatures and sediment loads in Big Sheep Creek impede migration of spring/summer Chinook. |
Water Quantity |
Decreased Water Quantity |
-- |
Dam or Hydropower Facility Management |
Water: Storage or Withdrawal |
Adults |
Low summer flows, exacerbated by irrigation diversions, impede migration of spring/summer Chinook into Big Sheep Creek. |