Protecting Public Health and the Environment.

Boise River (Lower) Subbasin

Subbasin at a Glance

Hydrologic Unit Code 17050114
Size 1,290 square miles (825,600 acres)

Water Bodies with EPA-Approved TMDLs (Category 4a)

Boise River, Lake Lowell

Beneficial Uses Affected Cold water aquatic life, salmonid spawning, domestic and agricultural water supply, primary and secondary contact recreation

Major Land Uses

Range, grazing, forest, agriculture, urban

Date Approved by EPA

January 2000
EPA Approval Letter
Date Approved by EPA Subbasin assessment only; not subject to EPA approval
Date Sediment and Bacteria Addendum Approved by EPA June 2008
EPA Approval Letter
Date Lake Lowell TMDL Addendum Approved by EPA December 2010
EPA Approval Letter
Date 2015 Sediment and Bacteria Addendum Approved by EPA September 2015
EPA Approval Letter
Date 2015 Total Phosphorus Addendum Approved by EPA December 2015
EPA Approval Letter

Subbasin Characteristics

The Lower Boise River subbasin is located in southwest Idaho. The lower Boise River itself is a 64-mile stretch that flows in a northwesterly direction through Ada and Canyon Counties and the cities of Boise and Caldwell. It originates at Lucky Peak Dam and flows into the Snake River near Parma. Major tributaries include Fifteenmile Creek, Mill Slough, Mason Creek, Indian Creek, Conway Gulch, and Dixie Drain.

1999 Subbasin Assessment and TMDL

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 wasteload 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 atmospheric conditions preclude compliance with cold water biota temperature criteria during June, July, and August.

The US 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.

1999 TMDL: Stream and Pollutants for Which TMDLs Were Developed

Lower Boise River
Sediment, bacteria

2001 Subbasin Assessment

Two segments of the lower Boise River are listed for nutrients on Idaho's 1998 §303(d) list and eight tributaries are listed for a variety of pollutants.

The Snake River-Hells Canyon TMDL is scheduled to be completed in 2001. Nutrients and sediment are listed as pollutants of concern in that TMDL and will be addressed by assigning load allocations to the major tributaries to the Snake River, including the lower Boise River. When the Snake River-Hells Canyon TMDL allocates a nutrient load to the lower Boise River, load reductions from the tributaries to the lower Boise River will be necessary to meet the Snake River-Hells Canyon load allocation.

2001 Summary of Assessment Outcomes

Water Body Listed Pollutants Recommendations
Lower Boise River Nutrients Delist for nutrients
Blacks Creek Dissolved oxygen, sediment, nutrients Delist for dissolved oxygen, sediment, nutrients
Fivemile Creek Dissolved oxygen, sediment, nutrients Delist for dissolved oxygen, sediment, nutrients; list for bacteria
Tenmile Creek Dissolved oxygen, sediment, nutrients Delist for dissolved oxygen, sediment, nutrients; list for bacteria
Mason Creek Dissolved oxygen, sediment, nutrients Delist for dissolved oxygen, sediment, nutrients; list for bacteria
Indian Creek Dissolved oxygen, oil and grease, sediment, nutrients, temperature Delist for nutrients, oil, and grease; no TMDL for dissolved oxygen or sediment, but leave on §303(d) list; temperature will be addressed in the future; list for bacteria
Sand Hollow Creek Dissolved oxygen, sediment, nutrients Delist for nutrients, oil and grease; no TMDL for dissolved oxygen or sediment, but leave on §303(d) list; temperature will be addressed in the future; list for bacteria

2008 Addendum

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.

2010 Addendum

This addendum addresses Lake Lowell in the Lower Boise River subbasin. The lake is impaired by dissolved oxygen and nutrients, and a TMDL was developed for total phosphorus to address these impairments. Identified sources of nutrients include phosphorus from agricultural runoff via canal and drain tributaries and waterfowl. Numeric water quality targets were set for Lake Lowell based on Idaho’s water quality standards and established targets for similar water bodies.

2010 Addendum: Water Bodies and Pollutants for Which TMDLs Were Developed

Lake Lowell
Total phosphorus

Subbasin Documents


Staff Contacts

Water Quality Manager
Lance Holloway
DEQ Boise Regional Office
1445 N. Orchard St.
Boise, ID 83706
(208) 373-0550
lance.holloway@deq.idaho.gov