Payette River (Lower) Subbasin

Subbasin at a Glance

Hydrologic Unit Code	17050122
Size	380,000 acres
§303(d) Listed Stream Segments	Lower Payette River (River Mile 38.5 to River Mile 0)
Beneficial Uses Affected	Cold water biota, primary contact recreation, secondary contact recreation, salmonid spawning
Pollutants of Concern	Nutrients, temperature, bacteria
Major Land Uses	Rangeland, irrigated agriculture
Date Approved by U.S. EPA	May 2000
Date Addendum Approved by U.S. EPA	July 2008 EPA Approval Letter

Overview

The lower Payette River is located in southwestern Idaho. Bissel Creek, also listed on the 1994 §303(d) list and located in the Lower Payette River TMDL project area, is addressed in a separate document.

The hydrology of the river is complex, with numerous irrigation water withdrawal and return drains dominating both the flow and quality of the river. The presence of Black Canyon Dam has greatly altered the amount and type of sediment in the lower Payette River originating from the upper watershed.

Fisheries studies conducted by the Idaho Department of Fish and Game in 1997 indicate many of the same species supported by the river in 1974 were also supported in 1997. Mountain whitefish is the dominant cold water species. Warm water species can be found throughout the river, with non-game species being dominant.

Sources of pollutants include both point sources and nonpoint sources. Point sources are limited mainly to municipal wastewater treatment plants and confined animal feeding operations. Nonpoint sources are associated with agricultural, urban, suburban, and rural areas.

Nutrients have not been shown to cause impairment to the beneficial uses in this water body at this time. While total phosphorus and nitrogen are at concentrations that could cause nuisance aquatic vegetation growth, data show they do not. While dissolved oxygen concentrations do not drop below the water quality standard, monitoring indicated that aquatic growth is causing a fluctuation in dissolved oxygen levels. If it is determined that the lower Payette River is a significant source of nutrients to the lower Snake River (in the lower Snake River/Brownlee TMDL), reduction targets for the lower Payette River will be addressed at that time.

Summer water temperatures in the lower Payette River are warm and exceed water quality standards for both cold water biota and salmonid spawning. However, it was determined that other factors, including habitat modification and flow alteration, were also significant causes of impairment of beneficial uses. In addition, warm water temperatures that exceed water quality standards originate from Black Canyon Reservoir. Because of these conditions, a temperature TMDL was not developed. TMDLs were also not written for flow alteration and habitat modification because these are not pollutants as described under Section 303(d) of the Clean Water Act.

Fecal coliform bacteria levels exceed the water quality standards for both primary and secondary contact recreation. Increasing levels are noted from Black Canyon Dam to the Snake River, with an exceedance of the water quality standards from river mile 25 to the confluence. Overall, a fecal coliform reduction of 84% will be required to achieve water quality standards. The load allocation will focus on nonpoint sources only. The overall contribution to the fecal coliform bacteria load from point sources (municipal wastewater treatment plants) is 0.005%. If the total elimination of bacteria from the point sources were to occur, a total load reduction of only 0.07% would be achieved. Therefore, any reduction from point sources would not impact the overall load to the lower Payette River.

Stream and Pollutant for Which TMDLs Were Developed

Lower Payette River: Bacteria

Department of
Environmental Quality

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