Boise River (Lower) Subbasin

Subbasin at a Glance

Hydrologic Unit Code	17050114
Size	1,290 square miles
§303(d) Listed Stream Segments	4 segments of the Boise River (Lucky Peak Dam to Barber Diversion, Barber Diversion to Star, Star to Notus, Notus to Snake River)
Beneficial Uses Affected	Cold water biota, primary and secondary contact recreation, domestic and agricultural water supplies, salmonid spawning
Pollutants of Concern	Flow alteration, sediment, dissolved oxygen, oil and grease, nutrients, bacteria, temperature
Major Land Uses	Forestry, agriculture, grazing, urban
Date Approved by U.S. EPA	January 2000
Date Sediment and Bacteria Addendum Approved by U.S. EPA	June 2008 EPA Approval Letter
Date Lake Lowell TMDL Addendum Approved by EPA	December 2010 EPA Approval Letter

Overview

The lower Boise River is a 64-mile stretch of river that flows through Ada County, Canyon County, and the city of Boise, Idaho. The river flows in a northwesterly direction from its origin at Lucky Peak Dam to its confluence with the Snake River near Parma, Idaho. Major tributaries include Fifteenmile Creek, Mill Slough, Mason Creek, Indian Creek, Conway Gulch, and Dixie Drain. View the subbasin assessment for these tributaries.

Of the seven listed pollutants, only sediment and bacteria require TMDLs. Pollutant targets are based on existing water quality criteria for bacteria and on a numeric interpretation of the state narrative standard for sediment. Because the lower Boise River is a major tributary to the lower Snake River, phosphorus (total and dissolved) will be examined for possible load and waste load allocations after completion and approval of the Snake River-Hells Canyon TMDL.

Load allocations for temperature are not recommended for the lower Boise River segments listed for temperature since it has been found that atmospheric conditions preclude compliance with cold water biota temperature criteria during June, July, and August.

The U.S. Environmental Protection Agency does not believe that flow (or lack of flow) is a pollutant as defined by the Clean Water Act. Since TMDLs are not required for water bodies impaired by pollution but not pollutants, a TMDL was not developed for flow alteration.

Stream and Pollutants for Which TMDLs Were Developed

Lower Boise River: Sediment, bacteria

Subbasin Documents

Lower Boise River TMDL Subbasin Assessment,Total Maximum Daily Loads (September 1999)
Sediment and Bacteria Allocations Addendum to the Lower Boise River TMDL (April 2008)
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 TMDL Five-Year Review (February 2009)
Lake Lowell TMDL: Addendum to the Lower Boise River Subbasin Assessment and Total Maximum Daily Loads (December 2010)

Department of
Environmental Quality

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