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Boise River (South Fork) Subbasin

Data Details
Size 1,306 square miles (835,645 acres)
Water Bodies with EPA-Approved TMDLs (Category 4a) Lime Creek, Smith Creek and tributaries
Beneficial Uses Affected Aquatic life support, contact recreation, water supply, wildlife habitats, aesthetics
Major Land Uses Predominantly uninhabited federal land managed by the US Forest Service; forestry, roads, mining, agriculture/livestock, recreation
Date Approved by EPA (2002 subbasin assessment) Subbasin assessment only; not subject to EPA approval
Date Approved by EPA (2008 TMDL) March 2009 EPA Approval Letter

Subbasin Characteristics

The South Fork Boise River subbasin is located in southwestern Idaho, east of Boise and predominantly in Elmore and Camas Counties. The watershed includes the South Fork Boise River upstream of the slack water of Arrowrock Reservoir, Anderson Ranch Reservoir, and all South Fork Boise River tributaries upstream to the headwaters. The subbasin area is primarily federally owned and administered. Prairie, Pine, and Featherville are the only recognized communities in the watershed that have year-round residents; second/summer/recreational homes are found in numerous subdivided areas throughout the watershed. Access is provided by many miles of US Forest Service-maintained roads and by county-owned or county-maintained roads.

2002 Upper Boise River Watershed Assessment

The upper Boise River watershed is made up of two subbasins, as summarized in the table below.

Hydrologic Unit Codes17050111 (North/Middle Fork Boise River Subbasin)
17050113 (South Fork Boise River Subbasin)
Size2,033 square miles (1,301,120 acres)
Beneficial Uses AffectedCold water aquatic life, salmonid spawning, primary and secondary contact recreation, domestic water supply
Major Land UsesForestry, roads, mining, agriculture/livestock, recreation

Located in southwestern Idaho, the upper Boise River watershed is about 2,033 square miles of predominantly undeveloped forestland and open range with both managed and free-flowing streams. The upper Boise River watershed is comprised of the two hydrologic cataloging units of the Boise River system upstream of Arrowrock Reservoir. The waters of the subbasin join to form the Arrowrock Reservoir, which supplies water to Lucky Peak Reservoir and the lower Boise River. This subbasin assessment found that all § 303(d)-listed water bodies within the upper Boise River watershed are currently fully supporting all of their beneficial uses and are no longer candidates for TMDL development. The subbasin assessment also lists water bodies not fully supporting their beneficial uses that should be added to the § 303(d) list during the next listing cycle.

2002 Summary of Assessment Outcomes on 1998 § 303(d) List

Not on 1998 § 303(d) List

Buck CreekSediment, nutrients, bacteria
Browns CreekSediment, nutrients
Willow CreekNutrients
South Fork Boise RiverNutrients
Deer CreekTemperature
Little Smoky CreekSediment, nutrients
Cayuse CreekSediment, nutrients
North Fork Feather CreekSediment, nutrients
Smith CreekSediment, nutrients, bacteria
Rattlesnake CreekSediment, nutrients
Crooked RiverSediment, nutrients
Beaver CreekSediment, nutrients
Rabbit CreekSediment, nutrients
Meadow CreekSediment, nutrients
French CreekSediment, nutrients
Little Camas ReservoirSediment, nutrients

2008 Subbasin Assessment and TMDL

The subbasin consists of 34 separate water body assessment units. Of these, 14 were identified as water quality limited and were placed on the 2002 § 303(d) list. Of these, five (listed below) are identified in the subbasin assessment as needing TMDLs to address temperature. Temperature is a water quality factor integral to the lifecycle of fish and other aquatic species. Elevated stream temperatures can be harmful to fish at all life stages. Sources of elevated temperature are anthropogenic alterations
related to roads, farming, grazing, mining, timber harvest, community or domestic development, or other activities that reduce stream shade or alter the stream in a way that results in increased stream temperatures. In addition, the subbasin assessment
identifies several streams to be added to the state’s list of impaired water bodies for flow and habitat alteration in the next Integrated Report and others to be removed for sediment and unknown pollutants.

2008 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Smith CreekTemperature
Lime CreekTemperature
North Fork Lime CreekTemperature
South Fork Boise RiverTemperature
Middle Fork Lime CreekTemperature
South Fork Lime CreekTemperature

This is an addendum to the Lower Boise River TMDL for sediment and bacteria approved by the US Environmental Protection Agency on January 25, 2000. The addendum provided the Avimor Development and the City of Kuna, Idaho, with wasteload allocations for total suspended solids and E. coli bacteria for a discharge to Dry Creek and Indian Creek, respectively. DEQ also outlines in this addendum the manner in which the sediment reserved for growth shall be allocated to new and existing sources in the future. The bolded changes in the addendum are made on pages 61, 62, 64, and 72 of the original document. Table 15 was revised in June 2012.

Subbasin Documents

  • Lower Boise River TMDL: Subbasin Assessment, Total Maximum Daily Loads (September 1999)
  • Lower Boise River Nutrient & Tributary Subbasin Assessments (December 2001)
  • Lower Boise River Nutrient Subbasin Assessment (December 2001)
  • Fivemile and Tenmile Creek Subbasin Assessment (December 2001)
  • Mason Creek Subbasin Assessment (December 2001)
  • Sand Hollow Creek Subbasin Assessment (December 2001)
  • Indian Creek Subbasin Assessment (December 2001)
  • Blacks Creek Subbasin Assessment (December 2001)
  • Lower Boise River Tributary Subbasin Assessment Appendices (May 2001)
  • Response to Comments Record Draft Lower Boise River Nutrient Subbasin Assessment (January 2002)
  • Sediment and Bacteria Allocations Addendum to the Lower Boise River TMDL (April 2008; revised June 2012 to account for wasteload allocations)
  • Implementation Plan for the Lower Boise River Total Maximum Daily Load (December 2003)
  • Lower Boise River Implementation Plan Total Phosphorus (December 2008)
  • Lower Boise River Total Phosphorus Implementation Plan Letter to EPA (July 2008)
  • Lower Boise River Total Phosphorus Implementation Plan Letter to EPA (January 2009)
  • Lower Boise River: TMDL Five-Year Review (February 2009)
  • Lake Lowell TMDL: Addendum to the Lower Boise River Subbasin Assessment and Total Maximum Daily Loads (September 2010)
  • Lake Lowell Watershed Total Maximum Daily Load Implementation Plan for Agriculture (June 2012)
  • Lower Boise River TMDL: 2015 Sediment and Bacteria Addendum (June 2015)
  • Lower Boise River TMDL: 2015 Total Phosphorus Addendum (August 2015)
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    DEQ Boise Regional Office
    1445 N. Orchard St.
    Boise, ID 83706
    Ph: (208) 373-0550
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