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Salmon Falls Creek Subbasin

DataDetails
Hydrologic Unit Codes17040213
Size863 square miles (552,320 acres) in Idaho
2,082 square miles (1,332,480 acres) total
Water Bodies with EPA-Approved TMDLs (Category 4a)Big Creek, Browns Creek, Cedar Creek, Cedar Creek Reservoir and tributaries, China Creek, Corral Creek, Cottonwood Creek, Devil Creek, Hot Creek, House Creek, North Fork Salmon Falls Creek, Player Creek, Salmon Falls Creek, Salmon Falls
Reservoir, Shoshone Creek
Beneficial Uses AffectedCold water aquatic life, salmonid spawning, secondary contact recreation
Major Land UsesRangeland, irrigated agriculture
Date Mid-Snake River TMDL Approved by EPAApril 1997 –
EPA approval letter
Date Modification Approved by EPASeptember 2005
Date Approved by EPAFebruary 2008
Date Approved by EPAOctober 2021 – EPA approval letter

Subbasin Characteristics

The Salmon Falls Creek subbasin is located in south-central Idaho. Water quality in the subbasin, in general, is of good to moderate quality. However, Salmon Falls Creek Reservoir is one of the few water bodies in the state with identified mercury contamination. Sediment, nutrients, and temperature are the most common listed pollutants throughout the subbasin.

1997 Middle Snake River Watershed Assessment and TMDL

Data Details
Hydrologic Unit Codes

17040212 (Upper Snake-Rock Subbasin)
17040213 (Salmon Falls Subbasin)

Size 94 square miles (60,160 acres)
Beneficial Uses Affected Aquatic life, primary and secondary contact recreation
Major Land Uses Irrigated agriculture, confined animal feeding operations, food processing, aquaculture, urban, hydroelectric development

1997 TMDL: Streams and Pollutant for Which TMDLs Were Developed

StreamPollutants
14 sections of the middle Snake River, including Bliss, Shoshone Falls, Upper Salmon Falls, and Lower Salmon Falls ReservoirsTotal phosphorus

Aquaculture Wasteload Allocations

Draft wasteload allocations for aquaculture facilities were developed in July 2004. These allocations are designed to meet the total phosphorus reductions as specified in the Middle Snake River and Upper Snake Rock TMDLs. The allocations affect 37 TMDLs for total phosphorus and total suspended solids and six associated segments of the Snake River.

Public comments were accepted on the document in August 2004. Based on the information and comments received, DEQ modified the document and resubmitted it for public comment in the following three parts:

2007 Subbasin Assessment and TMDL

In most of the listed assessment units, total phosphorus was a limiting nutrient. However, in the Big Creek and Cottonwood Creek watersheds, it was determined that total phosphorus was in excess and may be impacting the beneficial uses of Shoshone Creek.

While the majority of stream systems appear to have little impact from excess nutrients, the same cannot be said for the two reservoir systems. Both Cedar Creek and Salmon Falls Creek Reservoirs contain excess nutrients that lead to nuisance aquatic vegetation blooms. TMDLs were developed for the tributary systems that feed these two reservoirs. Only nonpoint sources and natural soil-associated phosphorus contribute to this increase in total phosphorus concentrations, as there are no point sources in the watershed.

In the lower section of Salmon Falls Creek, where ground water plays a significant role in the hydrology of the system, nitrogen was in excess and could lead to nuisance aquatic vegetation growths.

It is EPA policy that flow and habitat alterations are pollution and not specific pollutants, and TMDLs are not required. However, streams found to be impacted by these forms of pollution will remain on the §303(d) list. Cedar Creek below the Cedar Creek Reservoir falls into this category for flow alteration.

All streams listed for temperature were examined and require load reductions as a result of lack of shade.

Although not currently listed on the §303(d) list, Salmon Falls Creek Reservoir was examined due to a fish consumption advisory placed on the water body in 2001. Fish tissues were collected in October 2006. Mercury concentrations found in fish at that time averaged well above DEQ’s fish tissue criterion. In order to achieve the water quality standard, mercury levels need to be reduced by nearly 70%.

In addition, DEQ proposed removing the following water bodies from the state’s list of degraded waters for specific pollutants for which TMDLs have already been completed:

Lower Salmon Falls Creek: bacteria and dissolved oxygen
Shoshone Creek: bacteria
Hot Creek: sediment
Cottonwood Creek: dissolved oxygen

2007 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Lower Cedar Creek Temperature, sediment
Lower Salmon Falls Creek Temperature, nutrients, sediment
Devil Creek Temperature
Cedar Creek Reservoir Temperature, nutrients, sediment
China Creek, Corral Creek, Whiskey Slough Temperature, nutrients, sediment
Salmon Falls Creek Reservoir Mercury, nutrients
China Creek Temperature, nutrients, sediment
Salmon Falls Creek Temperature, nutrients, sediment
North Fork Salmon Falls Creek Temperature
Shoshone Creek Temperature, sediment
Hot Creek Temperature
Big Creek Temperature, nutrients, sediment
Cottonwood Creek Temperature, nutrients, sediment, bacteria

2021 Salmon Falls Creek Temperature TMDL

The Salmon Falls Creek Subbasin TMDL – 2021 Temperature TMDL updates TMDLs for twenty-four (24) assessment units that are currently in Category 4a with approve temperature TMDLs. The 2021 TMDL includes an updated Potential Natural Vegetation shade assessment using shade targets that are more appropriate than the targets used in the 2007 Salmon Falls Temperature TMDL.  Additionally, two assessment units evaluated during the development of this TMDL may be intermittent. Updated TMDLs were not completed on the assessment units that may be intermittent. Future assessments are needed to characterize the hydrology of the potentially intermittent AUs in the Salmon Falls Subbasin.

2021 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Stream Pollutants
Salmon Falls Creek Temperature
Devil Creek Temperature
House Creek Temperature
Cedar Creek Temperature
China, Browns, Corral, Player Creeks Temperature
North Fork Salmon Falls Creek Temperature
Shoshone Creek Temperature
Hot Creek Temperature
Big Creek Temperature
Cottonwood Creek Temperature

Subbasin Document(s)

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DEQ Twin Falls Regional Office
650 Addison Avenue West, Suite 110
Twin Falls, ID 83301
Ph: (208) 736-2190
Fax: (208) 736-2194
Toll Free: (800) 270-1663

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