Imnaha Subbasin Summary |
The Imnaha subbasin is located in the farthest northeastern corner of Oregon near the center of the Columbia Basin. Like the Grande Ronde, the Imnaha River flows in a northerly direction and is a direct tributary to the Snake River. The entire drainage is contained in U.S. Geological Survey (USGS) 4th field hydrologic unit code (HUC) 17060102 and joins the Snake River at river mile (RM) 191.7, approximately 48 river miles upstream of Lewiston, Idaho, and 3.4 miles upstream of the Salmon River confluence. The headwaters of the Imnaha River drain the eastern escarpment of the Wallowa Mountains and originate within the Eagle Cap Wilderness. At lower elevations, the Imnaha obtains flow from streams draining an adjacent plateau, which is located between the Wallowa River drainage to the west and Hells Canyon of the Snake River to the east. Ninety-eight percent of the subbasin lies within Wallowa County, with the remaining 2% split between Baker and Union counties. The subbasin is sparsely populated and contains only the small town of Imnaha (population 25) within its boundaries.
Source: Imnaha Subbasin Plan
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Status and Trends of Focal Species in Imnaha Subbasin |
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Species |
ESU |
MPG |
Population |
Biological Objective (s) |
Biological Status |
Federal Status |
Data / Charts |
Fall Chinook |
Snake River |
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Draft Recovery Plan Criteria : Unknown
Subbasin Plan Objective : 3,000 natural adults290
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Redd Counts
2009: 36 redds 143
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Threatened |
Status & Trends |
Spring Chinook |
Snake River |
Grande Ronde-Imnaha |
Imnaha, Big Sheep Creek |
Draft Recovery Plan Criteria : Unknown
Subbasin Plan Objective : 3,800 natural adults (5,740 total returns)290
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NOSA Estimate
2016: 607 spawners474
Redd Counts
2016: 524 redds (mixed)170
Juvenile Emigrants (natural)
2010: 145,179 juveniles (natural) 172
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Threatened |
Status & Trends |
Pacific Lamprey |
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Subbasin Plan Objective : None
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Unknown
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Species of Concern |
No Data |
Summer Steelhead |
Snake River |
Imnaha |
Imnaha |
Draft Recovery Plan Criteria : Unknown
Subbasin Plan Objective : 2,100 natural adults (4,315 toal returns)290
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Redd Counts
2016: Camp Creek - 40 redds35
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Threatened |
Status & Trends |
Bull Trout |
Imnaha |
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Imnaha River, Big Sheep Creek, Little Sheep Creek, McCully Creek |
Draft Recovery Plan Criteria : 5,000 adults (no delineation among local populations)291
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Redd Counts
2016: 235 redds141
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Threatened |
Status & Trends |
View abundance data for Imnaha Subbasin
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Hatcheries located in Imnaha Subbasin |
**Hatchery data will be updated in 2016** |
Hatchery / Acclimation Pond |
Hatchery Info |
Releases / Returns |
Program Reviews(APRE / HSRG / HGMP / USFWS) |
Map |
Imnaha Pond |
View |
View |
View |
View
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Irrigon Fish Hatchery |
View |
View |
View |
View
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Hatchery Releases and Returns to Imnaha Subbasin358 |
**Hatchery data will be updated in 2016** |
Some releases into subbasins may be from hatcheries located in other provinces and subbasins. Hatchery releases of anadromous fish, within the geographic range of an ESU/DPS, are listed accordingly. |
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Hatchery / Acclimation Pond |
Species |
ESU/DPS |
Released in 2009 |
Returns to Collection Facility in 2009 |
Data as of |
Imnaha Pond
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Spring Chinook |
Snake River Spring/Summer Chinook ESU |
234,963
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1,160
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8 / 30 / 2010
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Irrigon Fish Hatchery
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Rainbow Trout |
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163,066
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8 / 30 / 2010
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Summer Steelhead |
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45,298
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8 / 30 / 2010
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Lookingglass Fish Hatchery
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Spring Chinook |
Snake River Spring/Summer Chinook ESU |
58,839
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8 / 30 / 2010
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Recovery Status for ESA-Listed Salmon and Steelhead in the Imnaha Subbasin146, 177 |
Updated : 5/27/2010
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Species |
Population |
Abundance Threshold |
Mean Abundance |
Major Spawning Area |
Growth Rate |
Recruits / Spawners |
Current Viability |
Summer Steelhead |
Imnaha River |
1,000 |
Unknown |
Unknown |
Unknown |
Unknown |
Moderate |
Spring/Summer Chinook |
Imnaha River |
750 |
395 |
1 of 1 |
1.05 |
0.80 |
Low |
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Big Sheep Creek |
500 |
4 |
----- |
Unknown |
0.29 |
Functionally Extirpated |
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Limiting Factors in the Imnaha Subbasin 424, 425 |
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Key Limiting Factor |
Impairment |
Habitat Affected |
Threat Type |
Threat Name |
Life Stage(s) |
Description |
Habitat Quantity and Quality |
Access and Availability |
Freshwater-Instream |
Dam or Hydropower Facility Management |
Migration Impediments |
Juveniles, adults |
Seasonal barriers such as irrigation diversions in the Big Sheep Creek watershed impede migrations of bull trout. Diversions associated with the Wallowa Valley Improvement Canal have created barriers to migrating bull trout in Big Sheep, Little Sheep, and McCully creeks. |
Habitat Quantity and Quality |
Morphological Changes |
Freshwater-Floodplain |
Agricultural Practices; Urbanization |
Wetland Loss; Impervious Surfaces (Road Density); Riparian Degradation |
Juveniles, adults |
Modification through riprapped banks, dredging, and elimination of off-channel refugia has reduced or eliminated rearing habitat. |
Habitat Quantity and Quality |
Small-Scale Structural Complexity; Morphological Changes |
Freshwater-Riparian |
Agricultural Practices |
Riparian Degradation |
Juveniles, adults |
Cultivation, farming, and pasturing have reduced riparian habitat in many tributaries, especially in the Big Sheep Creek watershed. |
Habitat Quantity and Quality |
Small-Scale Structural Complexity; Morphological Changes |
Freshwater-Instream |
Agricultural Practices |
Riparian Degradation; Bank Destabilization |
Juveniles, adults |
Channels have attained unsuitable width:depth ratios, which create a shallow and wide system. |
Sediment Conditions |
Increased Sediment Quantity |
Freshwater-Instream |
Agricultural Practices; Forest Management |
Sediment: Bank Destabilization; |
All |
Increased sediment is a key attribute limiting bull trout production |
Water Quality |
Temperature |
-- |
Agricultural Practices; Forest Management |
Riparian Degradation |
All |
High water temperature is a key attribute limiting bull trout production |
Water Quantity |
Decreased Water Quantity |
-- |
Dam or Hydropower Facility Management |
Water: Storage or Withdrawal |
Eggs, adults |
Reduction of flows by irrigation deiversions limits spawning and incubation in Big Sheep Creek. |
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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 |
Erosion Control; Agricultural Practices; Urbanization |
Diking; Impervious Surfaces (Road Density); Riparian Degradation |
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; Wetland Loss |
Juveniles, Pre-spawn adults |
Pre-spawning Chinook are impacted by losses of habitat diversity and streambed instability in the lower reaches of the Imnaha. |
Instantaneous Mortality |
Anthropogenic Mortality |
-- |
Fishery Management |
Harvest |
Adults |
Fall Chinook are subject to both ocean and 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 |
Temperature |
-- |
Agricultural Practices |
Riparian Degradation |
Eggs, juveniles |
High temperatures affect the productivity of Chinook in the Lower Imnaha. |
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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. |
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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 steelhead productivity. |
Habitat Quantity and Quality |
Small-Scale Structural Complexity; Morphological Changes |
Freshwater-Instream |
Agricultural Practices; Forest Management |
Diking; Filling; Wood/Structure Removal; Wetland Loss |
Juveniles |
Lack of diverse, deep, and cool habitat types in the Big Sheep Creek and Little Sheep Creek watersheds limit steelhead fry colonization and summer rearing. |
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;+E64 Riparian Degradation; Bank Destabilization |
Eggs, juveniles |
Summer temperatures and sediment loads in Big Sheep Creek limit steelhead. |
Water Quantity |
Increased Water Quantity |
-- |
Forest Management |
Water: Runoff Coefficient Alteration |
All |
Frequent high flow events in the Big Sheep Creek and Little Sheep Creek watersheds resulting from modification of upland vegetation through timber harvest and fires have changed spawning substrate availability and disrupt steelhead incubation. |
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