Protecting Public Health and the Environment.

Walcott Lake Subbasin

Subbasin at a Glance

Hydrologic Unit Code 17040209
Size 3,638 square miles, (2,296,320 acres)

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

D16 drain, Duck Creek, East Fork Rock Creek, Rock Creek, Snake River and tributaries, South Fork Rock Creek, Spring Creek

Beneficial Uses Affected Salmonid spawning, cold water aquatic life
Major Land Uses Rangeland, nonirrigated agriculture
Date Approved by EPA

June 2000
EPA Approval Letter

Date Rock Creek  Addendum Approved by EPA

October 2000
EPA Approval Letter

Date Fall Creek Aquaculture Addendum Approved by EPA

March 2007
EPA Approval Letter

Date Rueger Springs Creek Aquaculture Addendum Approved by EPA

March 2007
EPA Approval Letter

Date Lake Walcott 2013 Addendum: Marsh Creek Approved by EPA

January 2015
EPA Approval Letter

Subbasin Characteristics

The general physical and biological characteristics of the Lake Walcott subbasin have a strong influence on the water quality of the subbasin. Additionally, the scattered population centers and land uses of the subbasin exert a significant influence on the water quality of the subbasin. Land use in the subbasin is predominantly rangeland and agricultural lands used for non-irrigated agriculture. Limited irrigated agriculture also exists in the subbasin where water is either pumped from the ground or diverted from the Snake River. The major population center of the subbasin is the Burley/Heyburn area.

2000 Subbasin Assessment and TMDL

This document describes eight water bodies that are listed on the 1996 and 1998 §303(d) lists prepared by the State of Idaho. Sediment is the most common listed pollutant in the subbasin. Sediment was a listed pollutant on all 1996 §303(d) listed water bodies within the subbasin. Other listed pollutants include nutrients, low dissolved oxygen, pesticides, oil and grease, flow alteration, and unknown causes.

2000 TMDL: Streams and Pollutants for Which TMDLs Were Developed

Snake River
Sediment
Rock Creek
Sediment
East Fork Rock Creek
Sediment
South Fork Rock Creek
Sediment
Milner Reservoir
Sediment, oil and grease, total phosphorus, dissolved oxygen

2006 Fall Creek TMDL

The intent and purpose of the Fall Creek TMDL is to establish water quality load allocations for sediment, nutrients, and bacteria in Fall Creek as part of the overall Lake Walcott TMDL. Fall Creek is not a §303(d)-listed water body but is described in the 2000 Lake Walcott TMDL as a “perennial stream feeding the Snake River in the Walcott Subbasin.”

The receiving water body to Fall Creek is the Snake River, which is §303(d) listed. Consequently, the Fall Creek TMDL is necessary to protect the beneficial uses of the Snake River as part of the Lake Walcott TMDL. The Fall Creek TMDL is not a TMDL modification of the Lake Walcott TMDL; it is an addition to the Lake Walcott TMDL and does not modify in any way the Lake Walcott TMDL that presently exists in the Snake River. Rather, the intent is to bring the aquaculture facilities associated with Fall Creek into alignment with the National Pollutant Discharge Elimination System General Aquaculture Permit so that wasteload allocations can be applied to these aquaculture facilities under the Lake Walcott TMDL to meet water quality provisions for the Snake River.

The TMDL establishes the allowable loadings or other quantifiable parameters for Fall Creek and thereby provides the basis for the state to establish water quality-based controls that should provide the pollution reduction necessary to achieve downstream water quality standards and beneficial uses of the Snake River.

2007 Rueger Springs Creek TMDL

The intent and purpose of the Rueger Springs Creek TMDL is to establish water quality load allocations for sediment, nutrients, and bacteria in Rueger Springs Creek as part of the overall Lake Walcott TMDL. Rueger Springs Creek is not a §303(d)-listed water body. However, it is generally described in the Lake Walcott TMDL as one of many “scattered springs … throughout the region.” The receiving water body of Rueger Springs Creek is the Snake River, which is §303(d) listed. Consequently, the Rueger Springs Creek TMDL is necessary to protect the beneficial uses of the Snake River as part of the Lake Walcott TMDL.

The Rueger Springs Creek TMDL is not a TMDL modification; it is an addition to the Lake Walcott TMDL and does not modify in any way the Lake Walcott TMDL. It does bring the aquaculture facility associated with Rueger Springs Creek into alignment with the National Pollutant Discharge Elimination System General Aquaculture Permit so that a wasteload allocation can be applied to this facility under the Lake Walcott TMDL and meet water quality provisions for the Snake River. The Rueger Springs Creek TMDL, therefore, is an iterative watershed management tool for implementing state water quality standards and is based on the relationship between pollution sources and instream water quality conditions.

The Rueger Springs Creek TMDL establishes the allowable loadings or other quantifiable parameters for Rueger Springs Creek and thereby provides the basis for the state to establish water quality-based controls. These controls should provide the pollution reduction necessary for Rueger Springs Creek to achieve downstream water quality standards and beneficial uses of the Snake River.

2013 Lake Walcott TMDL

This TMDL addendum has been developed to address the temperature- and bacteria-impaired water bodies in the Lake Walcott subbasin that have been placed on Idaho’s current §303(d) list. The Lake Walcott subbasin is in southern Idaho. Two reaches of Marsh Creek in the Lake Walcott subbasin were listed on the 1998 §303(d) list for unknown pollutants. It has been determined that the only impairments for these reaches are temperature and E. coli. Additional water bodies in the subbasin are listed but not addressed in this addendum for various reasons.

2013 TMDL: Stream and Pollutants for Which TMDLs Were Developed

Marsh Creek
Temperature, E. coli

Subbasin Documents


Staff Contacts

Water Quality Manager
Kiley Mulholland
DEQ Twin Falls Regional Office
650 Addison Avenue West, Suite 110
Twin Falls, ID 83301
(208) 736-2190
kiley.mulholland@deq.idaho.gov