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Little Salmon River Subbasin

Data Details
Hydrologic Unit Codes 17060210
Size 576 square miles (368,640 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a) Big Creek, East Branch Goose Creek, Goose Creek, Little Salmon River, Mud and Little Mud Creeks
Beneficial Uses Affected Cold water aquatic life, salmonid spawning, primary contact recreation, domestic water supply
Major Land Uses Forestry, rangeland (grazing), recreation
Date Approved by EPA March 2006
Addendum Approved by EPA April 2013 EPA Approval Letter

Subbasin Characteristics

The Little Salmon River subbasin lies entirely in central Idaho. It originates at about 6,280 feet off of Blue Bunch Ridge. The watershed is 45 miles long, and the river flows north for 51 miles to its confluence with the Salmon River at Riggins. US Highway 95 parallels most of the river.

2006 Subbasin Assessment and TMDL

The Little Salmon River from Big Creek to Round Valley Creek was found to have beneficial uses impaired by temperature, nutrients, and bacteria. TMDLs were developed for these pollutants. Potential natural vegetation (shade) was used as a surrogate for temperature to achieve natural background conditions.

The Little Salmon River from Vicks Creek to Big Creek was found to have beneficial uses impaired by temperature. A TMDL was developed for temperature.

Big Creek was listed for an unknown pollutant. Elevated nutrient and bacteria levels were found in the creek. TMDLs were developed for nutrients and bacteria.

The Little Salmon River from Round Valley Creek to the mouth showed support of beneficial uses. However, DEQ was unable to analyze the effect of coarse sediment in the system. DEQ proposes to list the Little Salmon River from Round Valley Creek to the mouth for habitat alteration and delist it for sediment on the basis of DEQ Beneficial Use Reconnaissance Program scores that did not indicate impairment and on low suspended sediment data. However, the listing for habitat alteration is in recognition that the system was changed due to highway construction and the channel remains constricted, leading to potential coarse sediment loading problems. Idaho’s antidegradation policy applies in this case and existing uses must be maintained and protected from any activities that would result in human-caused excess sediment delivery to the system.

Elk Creek, Indian Creek, and Shingle Creek were all listed for sediment. Beneficial uses were fully supported in these watersheds and TMDLs are not necessary.

Brundage Reservoir was monitored weekly for temperature from early July through mid-August 2005. Monitoring occurred in late afternoon and early evening when reservoir temperatures would be highest. No violations of the cold water temperature standard were seen. Brundage Reservoir is proposed for delisting for temperature.

Goose Creek was assessed as part of DEQ’s BURP program and was found to have impaired beneficial uses. Goose Creek is proposed for listing on the next §303(d) list for an unknown pollutant. Lack of flow may be a causal factor in impairment of beneficial uses for Goose Creek. Therefore, a TMDL was not developed at this time. DEQ did not have the time during the writing of this TMDL to characterize the flows in Goose Creek to determine if intermittence was impairing beneficial uses.

2006 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Little Salmon River (Big Creek to Round Valley Creek) Temperature, bacteria, nutrients
Little Salmon River (Vicks Creek to Big Creek) Temperature
Big Creek Bacteria,nutrients

2013 Addendum

The Little Salmon River Subbasin Assessment and Total Maximum Daily Load Five-Year Review presented data showing that East Branch Goose Creek (ID17060210SL010_04) exceeded state water quality standards for bacteria and that the lowermost reach of Mud Creek (ID17060210SL008_03) had impaired water quality due to sediment from streambank erosion. This addendum determined the pollutant reductions necessary to support beneficial uses and meet water quality standards for each of these assessment units. Mud Creek requires a 22% sediment reduction, and East Branch Goose Creek requires a 57% bacteria reduction. These reductions represent very conservative calculations to ensure beneficial uses will be supported when pollutant loading is at its highest. Water quality standards should be met within a 5–15 year time period, depending on implementation strategies chosen for these assessment units.

2013 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Mud and Little Mud Creeks Sediment
East Branch Goose Creek Bacteria (E. coli)

Subbasin Document(s)

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DEQ Boise Regional Office
1445 N. Orchard St.
Boise, ID 83706
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