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Big Lost River Subbasin

Data Details
Hydrologic Unit Code 17040218
Size 2,452 square miles (1,569,161 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a) Antelope Creek, Bear Creek, Big Lost River, Bridge Creek, Cherry Creek, Corral Creek, East Fork Big Lost River, Leadbelt Creek, Lower Pass Creek, North Fork Big Lost River, Sage Creek, Star Hope Creek, Summit Creek, Thousand Springs Creek, Warm Springs Creek, Wildhorse Creek
Beneficial Uses Affected Cold water aquatic life, salmonid spawning, primary and secondary contact recreation, drinking water supply
Major Land Uses Livestock grazing, recreation, agriculture, and transportation (roads)
Date Approved by EPA August 2004 Approval Letter
Addendum Approved by EPA December 2011 EPA Approval Letter
Date Temperature TMDL – 2019 Addendum and Five-Year Review approved by EPA June 2019 Approval Letter

Subbasin Characteristics

The Big Lost River subbasin, isolated from surface connection with the Snake River, is one of four watersheds in central Idaho known as the Sinks Drainages. Surface flow not used for irrigation infiltrates to ground water, which moves southwest toward the Thousand Springs reach of the Snake River near Hagerman, Idaho, where spring flow emerges. Native fish populations, water quality, and riparian habitat conditions are issues of concern in the subbasin. The cumulative effects of irrigation diversion, alteration of vegetation by grazing in riparian areas, human-caused stream alterations, historic mining practices, roads, residential and municipal development, and past timber harvest have combined to impact water quality and aquatic life in the watershed

2004 Subbasin Assessment and TMDL

Twelve TMDLs were developed to address issues of temperature exceedance of water quality standards on eleven streams (two segments on Antelope Creek). Sediment TMDLs were prepared for the streams with temperature exceedances with the exception of Warm Springs Creek and the main stem Big Lost River from its origin at the confluence of the North and East Forks of the Big Lost River to Chilly Buttes. Sediment TMDLs were prepared for two additional streams that did not have sufficient temperature data to determine TMDLs for thermal loading: Twin Bridges Creek and Thousand Springs Creek.

TMDLs were not prepared for habitat and flow alteration. These are considered “pollution,” not “pollutants,” and TMDLs are not required for water bodies impaired by pollution. A TMDL is only required when a pollutant can be identified and in some way quantified.

2004 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Streams Pollutants
East Fork Big Lost River Sediment, temperature
Corral Creek (East Fork Big Lost tributary) Sediment, temperature
Starhope Creek Sediment, temperature
Wildhorse Creek Sediment, temperature
North Fork Big Lost River Sediment, temperature
Summit Creek Sediment, temperature
Big Lost River: Source to Chilly Buttes Temperature
Twin Bridges Creek Sediment
Thousand Springs Creek Sediment
Warm Springs Creek Temperature
Antelope Creek (two segments) Sediment, temperature
Bear Creek Sediment, temperature
Cherry Creek Sediment, temperature

2011 Addendum

This document was developed to address 14 assessment units (AUs) listed in Category 5 for impaired waters on Idaho’s 2010 Integrated Report. Additional unlisted AUs were evaluated for possible temperature violations. Investigation by DEQ showed that excess sediment was determined to be impairing water quality in two reaches of the Big Lost River: the reach above Bartlett Point Road and the reach above Mackay Reservoir. Sediment water quality targets were met in Bear, Pinto, Grant, and Garden Creeks. Bacteria was found to exceed the target for supporting secondary contact recreation as a beneficial use in Sage Creek; Wildhorse Creek was found to be meeting bacteria water quality targets. Investigation also showed that all streams examined for temperature impairment lacked shade to some degree. Potential natural vegetation TMDLs were completed for AUs of the Big Lost River, East Fork Big Lost River, Antelope Creek, Leadbelt Creek, Twin Bridges Creek, and the Thousand Springs Creek tributaries.

2011 Addendum: Streams and Pollutants for Which TMDLs Were Developed

Streams Pollutants
Antelope Creek Temperature
Big Lost River Temperature
East Fork Big Lost River Temperature
Leadbelt Creek Temperature
Sage Creek Temperature
Thousand Springs Creek tributaries Temperature
Twin Bridges Creek Temperature

Subbasin Documents

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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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