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Sheep Creek Watershed TMDL Development

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Main Page          Monitoring and Assessment          TMDL Development          Restoration and Protection          


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What is a TMDL?

A total maximum daily load (TMDL) is the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards. A TMDL can often be calculated using a simple equation that involves streamflow and pollutant concentration to express the allowable load in pounds per day, although the TMDL can also be expressed as a percent reduction in loading.


Why DEQ Writes TMDLs

The state of Montana monitors its waters and conducts water quality assessments to determine if waterbodies are supporting their designated uses. All waterbodies in the Sheep Creek project area must be maintained suitable for aquatic life, drinking water, agricultural, industrial, and recreational uses. Waters that are determined not to be supporting their designated uses are called impaired and are placed on Montana’s list of impaired waters. Impaired waterbodies and their associated probable causes and sources of impairment are published within Montana’s biennial Water Quality Integrated Report


Montana’s state law, and the federal Clean Water Act, require development of total maximum daily loads (TMDLs) for all waterbodies impaired by a pollutant (e.g., metals, nutrients, sediment, temperature). Sheep Creek was determined to be impaired for both aluminum and Escherichia (E. coli) and TMDLs have been developed for both impairments (see table below). 

TMDL development includes four main steps, which were followed in development of these TMDLs:

  • Characterizing the impaired waterbody’s existing water quality conditions and comparing those conditions to Montana’s water quality standards. During this step, measurable target values are set to help evaluate the stream’s condition in relation to the applicable water quality standards.

  • Quantifying the magnitude of the pollutant contribution from each significant source

  • Determining the total allowable load of the pollutant to the waterbody (the TMDL)

  • Allocating the total allowable pollutant load into individual loads for each significant source (referred to as load allocations for nonpoint sources and wasteload allocations for point sources)


TMDLs Written for Sheep Creek


Waterbody & Location Description


TMDL Status

TMDL Document

Sheep Creek,

Headwaters to mouth (Smith River)


Assessment Unit MT41J002_030



Sheep Creek Aluminum TMDL - December 2020

Found at:


E. coli


Sheep Creek E. coli TMDL and Water Quality Improvement Plan – September 2017

Found at:




Project Contacts





TMDL Project Manager - Aluminum and E. coli

Lou Volpe


(406) 444-6742


Page Last Updated: January 11, 2021