| Data | Details |
|---|---|
| Hydrologic Unit Codes | 17040213 |
| Size | 863 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 Affected | Cold water aquatic life, salmonid spawning, secondary contact recreation |
| Major Land Uses | Rangeland, irrigated agriculture |
| Date Mid-Snake River TMDL Approved by EPA | April 1997 – EPA approval letter |
| Date Modification Approved by EPA | September 2005 |
| Date Approved by EPA | February 2008 |
| Date Approved by EPA | October 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) |
| 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
| Stream | Pollutants |
|---|---|
| 14 sections of the middle Snake River, including Bliss, Shoshone Falls, Upper Salmon Falls, and Lower Salmon Falls Reservoirs | Total 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:
- Upper Snake Rock TMDL Modification Part 1 (February 2004)
- Upper Snake Rock TMDL Modification Part 2 (April 2005)
- Upper Snake Rock TMDL Modification Part 3 (May 2005)
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 |
2022 Salmon Falls Creek Subbasin Assessment and Total Maximum Daily Load Five-Year Review
The 5-year review of the Salmon Falls Creek subbasin assessment and total maximum daily loads (TMDLs) addresses the water bodies, or assessment units (AUs), in Category 4a of Idaho’s most recent federally approved Integrated Report. A review of data collected in 2019 confirms that the subbasin’s TMDL targets, set in 2007 and 2021, are still relevant. The analysis reflects an overall trend toward decreased levels of total suspended solids, sediment, and total nitrogen (Table C) in the subbasin. Total phosphorus still is high in some AUs. The 5-year review does not analyze all TMDLs for temperature; this analysis is provided in the 2022 Salmon Falls Creek Subbasin Assessment and Total Maximum Daily Loads Five-Year Review.
Subbasin Document(s)
- Middle Snake River Watershed Management Plan: Phase 1 TMDL Total Phosphorus (January 1997)
- Upper Snake Rock Implementation Plan (June 2001)
- Salmon Falls Creek Subbasin Assessment and Total Maximum Daily Loads (December 2007)
- Salmon Falls Creek Subbasin Agriculture TMDL Implementation Plan (February 2009)
- Salmon Falls Creek Subbasin Temperature TMDLs (July 2021)
- Salmon Falls Creek Subbasin Assessment Total Maximum Daily Load Five-Year Review (November 2022)
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