Lochsa River Subbasin
Subbasin at a Glance
|Hydrologic Unit Code||17060303|
|Size||1,180 square miles (755,200 acres)|
|Beneficial Uses Affected||Cold water aquatic life, salmonid spawning|
|Major Land Uses||Forest|
|Date Approved by EPA||Subbasin assessment only; not subject to EPA approval|
|Addendum||Submitted May 2012, revised October 2012|
|Date Temperature TMDL Approved by EPA||August 2018
The Lochsa River subbasin encompasses predominately undeveloped forestland and free-flowing streams. Most of the Lochsa River itself is designated as a Wild and Scenic River, and approximately half of the subbasin lies in the Selway Bitterroot Wilderness Area. The streams in the subbasin are home to a variety of fish, including Chinook Salmon, steelhead, Mountain Whitefish, and Bull Trout.
1999 Subbasin Assessment
Twenty-five tributary stream segments were §303(d) listed for sediment. Available data show that the sediment concentrations in the streams are within the normal range that is expected in the subbasin. Data also show that all 25 listed tributary stream segments support their beneficial uses. DEQ recommends all the segments be delisted for sediment.
The Lochsa River and one tributary stream segment were §303(d) listed for temperature. DEQ reviewed habitat, fish, and temperature data and concluded that, while water temperatures do exceed the state's criteria during parts of the year, these exceedances are natural and the river and its tributaries support their designated uses. DEQ recommends that the Lochsa River and the one tributary listed for temperature be removed from the §303(d) list for temperature.
As all listed stream segments were recommended for delisting, no TMDLs were developed in this 1999 subbasin assessment.
2012 Lochsa Temperature TMDL
The 2012 Lochsa Temperature TMDL established TMDLs for 37 assessment units (AUs) within the Lochsa River watershed. Six of the 37 AUs in the TMDL were included in Category 5 of Idaho’s 2014 Integrated Report. The TMDL analysis establishes water quality targets and load capacities, estimates existing pollutant loads, and allocates load reductions needed to return listed waters to a condition meeting water quality standards.
- Lochsa River Subbasin Assessment (September 1999)
- Lochsa River Subbasin Temperature Total Maximum Daily Loads: Addendum to the Lochsa River Subbasin Assessment (April 2012; Revised October 2012)