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Lemhi River Subbasin

Data Details
Hydrologic Unit Codes 17060204
Size 1,260 square miles (806,676 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a) Bohannon Creek, Canyon Creek, Eighteenmile Creek, Geertson Creek, Kenney Creek, Kirtley Creek, Lemhi River, Little Eightmile Creek, McDevitt Creek, Sandy Creek, Wimpey Creek
Beneficial Uses Affected Salmonid spawning, cold water aquatic life, primary and secondary contact recreation
Major Land Uses Livestock grazing, irrigated agriculture, recreation
Date Approved by EPA March 2000 EPA Approval Letter
Date Addendum Approved by EPA February 2013 EPA Approval Letter

Subbasin Characteristics

The Lemhi River subbasin is located in east-central Idaho with its terminus at the Salmon River in Salmon, Idaho. The subbasin falls entirely within Lemhi County, Idaho.

The Lemhi River has been identified as providing critical spawning and rearing habitat for two federally protected anadromous fish species: steelhead trout and spring/summer Chinook Salmon. The Lemhi River and its tributaries also provide important historic and/or current habitat for federally protected resident and migratory Bull Trout as well as Westslope Cutthroat Trout, which have been petitioned for listing under the Endangered Species Act.

1999 Subbasin Assessment and TMDL

TMDLs have been developed to address sediment in Bohannon Creek, Eighteenmile Creek, Geertson Creek, Kirtley Creek, Sandy Creek, McDevitt Creek, and Wimpey Creek and to address fecal coliform bacteria in the Lemhi River. Though Bohannon, Eighteenmile, Geertson, Hawley, Mill, Sandy, and Wimpey Creeks are listed for nutrients as well, no conditions within the streams have been observed that necessitate TMDLs for nutrients based on narrative state water quality standards.

The primary anthropogenic source of sediment having a deleterious effect on beneficial use support status within the seven streams listed for sediment was identified as sediment from streambank erosion. Excessive sedimentation is reducing the quality of spawning and rearing habitat for resident trout species and exceeds the same habitat parameters for anadromous species. Fecal coliform bacteria loading threatens primary and secondary contact recreation in the Lemhi River. Altered flow conditions resulting from diversion of surface waters for irrigation have eliminated migratory components of resident fish species and have elevated risks to isolated fish populations.

1999 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Lemhi River Fecal coliform bacteria
Bohannon Creek Sediment
Eighteenmile Creek Sediment
Geertson Creek Sediment
Kirtley Creek Sediment
McDevitt Creek Sediment
Sandy Creek Sediment
Wimpey Creek Sediment

2012 Addendum

This document addresses the assessment units (AUs) listed in Category 5 for impaired waters on Idaho’s 2010 Integrated Report. This document examines water quality status for these AUs and summarizes completed or ongoing watershed improvement projects in the subbasin. The TMDL analyses quantify pollutant loads and allocate load reductions needed to return listed waters to a condition meeting water quality standards.

The 1999 TMDL allocated load reductions for sediment for Bohannon, Eighteenmile, Geertson, Kirtley, McDevitt, Sandy, and Wimpey Creeks; for bacteria for the Lemhi River; and for temperature for Kirtley Creek. Based on EPA approval of these TMDLs, and after conversion of the stream segments into AUs for the Integrated Report, the 2010 Integrated Report lists these TMDLs as applying to 23 stream segments, listed in Category 4a for “Total Maximum Daily Load Completed and Approved.”

Some AUs were left in Category 5 of the 2008 and 2010 Integrated Reports due to converting from 1998 §303(d) list “water quality limited segments” to AUs based on GIS stream order analysis. Another administrative issue that caused listed segments to carry over to the 2010 Integrated Report was that some of the AUs still listed in Category 5 for unknown pollutants had already been determined to be impaired by sediment and were previously placed in Category 4a of the 2008 Integrated Report for completed TMDLs. Three AUs of the Lemhi River were added to the 2010 Integrated Report for suspected temperature impairment. Additional AUs were added to the 2010 Integrated Report through biological and habitat assessment results from DEQ Beneficial Use Reconnaissance Program monitoring. The 2nd-order segment of Eighteenmile Creek was listed for combined biota/habitat bioassessments but was determined to be impaired for temperature through the potential natural vegetation temperature TMDL process.

Further investigation by DEQ showed that some listed AUs have been historically dewatered year-round except for overflow put back in the channel when it was not required for irrigation and should more appropriately be listed in Category 4c for low flow alteration. At this time, the land uses of these streams are becoming increasingly driven by the restoration efforts of the Upper Salmon Basin Watershed Project to re-establish streamflow in the old channels and reconnect the streams with the Lemhi River. Temperature was determined to be impairing water quality in 18 AUs, including 7 AUs that had not previously been listed in Category 5, and temperature load allocations are provided in this document. E. coli was determined to be impairing water quality in one AU and a bacteria TMDL is provided for restoring beneficial uses to this AU.

2012 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Lemhi River Temperature
Eighteenmile Creek Temperature
Canyon Creek Bacteria (E. coli)
Little Eightmile Creek Temperature
Sandy Creek Temperature
Bohannon Creek Temperature
Kirtley Creek Temperature (revision of previous TMDL)

Subbasin Document(s)

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DEQ Idaho Falls Regional Office
900 N. Skyline Drive, Suite B
Idaho Falls, ID 83402
Ph: (208) 528-2650
Fax: (208) 528-2695
Toll Free: (800) 232-4635

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