Protecting Public Health and the Environment.

Clark Fork River (Lower) Subbasin

Subbasin at a Glance

Hydrologic Unit Code 17010213
Size 247 square miles (158,080 acres)

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

Cascade Creek, Clark Fork River, Dry Creek, East Fork Creek, Johnson Creek, Lightning Creek and tributaries, Mosquito Creek, Rattle Creek, Savage Creek, Twin Creek, Wellington Creek

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

Major Land Uses

Forestry, agriculture, rural residential, recreation
Date Approved by EPA

October 2007
EPA Approval Letter

Dates Clark Fork-Pend Orielle TMDL Approved by EPA

April 2001
EPA Approval Letter

September 2000
EPA Approval Letter

Subbasin Characteristics

Primarily located in Montana, the 320-mile long Clark Fork River flows from near Butte, Montana, to Lake Pend Oreille in Idaho. The Clark Fork River drains approximately 22,000 square miles in western Montana and northern Idaho, 247 square miles of which comprise the Lower Clark Fork subbasin in northern Idaho. The river drains into the 95,000-acre Lake Pend Oreille, and as the lake’s largest tributary, the Clark Fork River contributes approximately 92% of the annual inflow to the lake and most of the annual suspended sediment load.

2007 Subbasin Assessment and TMDL

This document addresses the lower-most 247 square miles of the subbasin located in north Idaho.

The Lower Clark Fork subbasin includes 180 miles of perennial streams. The river itself flows from east to west. With approximately 75% of the subbasin in public ownership, there is a diversity of recreational opportunities and wildlife. The river’s main tributary, Lightning Creek, harbors a regionally significant Bull Trout population and supports many other native fish.

Located just downstream from the Montana/Idaho border 10 miles before the river enters Lake Pend Oreille is AVISTA’s Cabinet Gorge Dam. The Cabinet Gorge Reservoir has a storage capacity of 105,000 acre-feet at full pool.

Metals and total dissolved gas pollution are the pollutants of concern in the main stem Clark Fork River. Intensive mining around the headwaters of the Clark Fork River in Montana left residues of heavy metals behind, which still pose a risk to water quality throughout the basin. Total dissolved gas supersaturation caused by the entrainment of gas in the water when spill occurs at a hydroelectric facility can remain high for significant distances downstream from the facility. Cabinet Gorge Dam has a capacity of approximately 36,000 cubic feet per second. When river flows exceed this capacity, excess flow spills. Entrained gases from these spills can remain in the water column into Lake Pend Oreille and the Pend Oreille River.

Temperature is identified as a pollutant in the lower Clark Fork River below the Idaho/Montana border. However, the lower Clark Fork River on the Montana side of the border has not been found to violate Montana water quality standards for temperature.

Sediment and temperature are the pollutants of concern in the tributaries to the lower Clark Fork River. Thick glacial outwash sediments in steep drainages combined with timber harvest and road construction have created potential sediment problems in several of the tributaries to the Clark Fork River. Temperatures exceed water quality standards for salmonid spawning throughout the subbasin. Fire and historic timber harvest have created a more open canopy and related stream warming compared to background conditions.

TMDLs were developed for each stream determined to not fully support beneficial uses in accordance with state of Idaho water quality standards. The TMDLs included in this document address in-stream sediment, metal, and temperature reduction goals to maintain or restore cold water aquatic life and salmonid spawning in the tributaries. The TMDLs help quantify needed improvements and target management actions to address water quality improvement measures and timelines.

2007 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Clark Fork River
(main stem in Idaho)
Metals, total dissolved gas
Cascade Creek
Dry Creek
Mosquito Creek
Twin Creek
Sediment, temperature
East Fork Creek
Sediment, temperature
Johnson Creek
Sediment, temperature
Lightning Creek
Sediment, temperature
Rattle Creek
Sediment, temperature
Savage Creek
Sediment, temperature
Wellington Creek
Sediment, temperature

2001 Clark Fork–Pend Oreille Watershed Assessment and TMDL

This watershed spans two subbasins and is summarized in the table below.

Hydrologic Unit Codes 17010213 (Lower Clark Fork Subbasin)
17010214 (Pend Oreille Lake Subbasin)
Size 25,000 square miles (16,000,000 acres) in Idaho and Montana
Beneficial Uses Affected Cold water aquatic life, salmonid spawning, warm water biota, primary contact recreation, secondary contact recreation, agricultural water supply, industrial water supply, domestic water supply

Major Land Uses

Agriculture, grazing, roads, hydropower, mining, timber harvest, urban, recreation

* These water bodies are located in the Lower Clark Fork subbasin (hydrologic unit code 17010213). They are analyzed in the 2007 Clark Fork/Pend Oreille subbasin assessment document and are assigned TMDLs in the Lower Clark Fork River subbasin assessment and total maximum daily loads discussed on this page.

The Clark Fork-Pend Oreille watershed lies in western Montana, northern Idaho, and northeastern Washington. The watershed is the source of the water that enters and leaves Lake Pend Oreille, the largest and deepest natural lake in Idaho. Inflow and outflow of the lake are regulated by hydroelectric facilities.

The Pend Oreille portion of this subbasin assessment examined 11 streams, 1 major river, and 2 lakes. Of the 11 streams, 5 were water quality impaired and required load allocations, primarily for sediment. Both Lake Pend Oreille and the Pend Oreille River were found to fully support their beneficial uses and were recommended for delisting.

The Clark Fork portion of this subbasin assessment was tabled until its scheduled assessment date in 2004. Insufficient time to complete the assessment and the prospect of more data available at that time drove this decision.

2001 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Cocolalla Creek (lower)
Cocolalla Creek (upper)
North Fork Grouse Creek
Hoodoo Creek
Pack River
Cocolalla Lake

Subbasin Documents

Staff Contacts

Surface Water Quality Manager
Bob Steed
DEQ Coeur d'Alene Regional Office
2110 Ironwood Parkway
Coeur d'Alene, ID 83814