The limiting factors included for each subbasin comprise the issues that limit fish production and their causes that deserve broad recognition. A comprehensive list of limiting factors is provided in the respective subbasin plan.
Limiting Factor Type
Type Description
Limiting Factor
Flows
Reduce production area and contribute to elevated temperatures
The annual hydrograph has been modified. Natural flow regime (flip-flop management) changes result in 7 different flow regimes on the mainstem Yakima and Naches rivers. Upstream of Union Gap, the hygrograph has been “flattened” affecting riparian and ecosystem function, productivity, and stability. Annual flow is reduced from Parker to Toppenish Creek/Marion Dam. Sustained high flows in the upper Yakima downstream to Union Gap and sustained low flows to lower Naches and from Union Gaap downstream limit habitat diversity. Low flows are problematic throughout the subbasin.
Instream Habitat
Cobble size/embeddedness, lack of large woody debris, etc. impair survival & reproduction
Summer/early-fall habitat availability is low or eliminated by low flow and high temperature in the lower Yakima River and Wapato Reach. Lack of habitat diversity and large woody debris is problematic throughout the subbasin. Excessive growth of in-channel aquatic vegetation in the lower/middle Yakima is problematic.
Passage Impediments
Dams, culverts, elevated water temperatures prevent necessary migration
Partial or total flow/temperature blockages to fish migrations due to diversions exist throughout the subbasin. Wenas Dam prevents access to the upper Wenas Creek and dewaters lower Wenas Creek. Migratory fish cannot access Umtanum Creek upstream of river mile 4.8 due to a gabion structure. Kachess, Keechelus, and Cle Elum dams prevent access to high elevation areas for spring Chinook, steelhead, and sockeye. Kokanee entrainment occurs at Rimrock Lake.
Predation
Reduces available spawners and harvest opportunity
Avian and fish predation problems exist throughout the subbasin. Grazing impacts affect bull trout during spawning periods.
Riparian Habitat
Lack of riparian vegetation contributes to elevated temperatures, turbidity, etc.
Riparian communities (particularly black cottonwood) in the mainstem Yakima and Naches rivers are degraded due to changes in the hydrograph. Channel incision has disconnected Toppenish Creek from the floodplain below Simcoe Creek. Riparian vegetation in Toppenish Creek between Unit II Pump Canal and Star Route 22 has been modified by grazing and irrigated agriculture. Problems associated with channel incision, bank stability, and riparian vegetation removal exist throughout the subbasin.
Water Quality
Includes temperature, dissolved oxygen, turbidity, pollutants, gas supersaturation
Elevated summer temperatures exist in lower reaches of tributaries and headwaters due to development, forest management, and grazing practices. Temperatures in the lower Yakima and Wapato Reach have increased to a point that returning fall-run adults must delay river entry and juveniles must migrate from the river earlier. The mainstem Middle Fork, North Fork, West Fork Teanaway River, and Stafford Creek are 303(d) listed for water temperature. Elevated sediment loads exist throughout the subbasin due to high road densities, increases in peak flows, bank erosion, and floodplain loss. High toxic pollutant levels exist in sediments throughout the subbasin.
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