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Total Maximum Daily Loads (TMDLs)

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Environment, Great Lakes, and Energy

Total Maximum Daily Loads (TMDLs)

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When a lake or stream does not meet Water Quality Standards (WQS), a study must be completed to determine the amount of a pollutant that can be put in a water body from point sources and nonpoint sources and still meet WQS, including a margin of safety. A TMDL is a document that describes the process used to determine how much pollutant load a lake or stream can assimilate.

TMDL Watersheds Screening Tool showing aerial imagery of Michigan with outlines of TMDL watersheds

DRAFT TMDLs Open for Public Comment


Frequently Asked Questions

What are Water Quality Standards?

Water Quality Standards are state rules established to protect the Great Lakes, the connecting waters, and all other surface waters of the state. These rules define the water quality goals for a lake or stream. You can read the Water Quality Standards here (Part 4 Rules). The water quality goals are in three areas:

  1. Uses of the lake or stream, such as swimming and fishing.
  2. Safe levels to protect the uses, such as the minimum oxygen level needed for fish to live; and
  3. Procedures to protect high quality waters.

Why are TMDLs being developed?

TMDLs are required by the federal Clean Water Act for water bodies that do not meet WQS.

How is it decided which water bodies need TMDLs?

Each state identifies water bodies within its boundaries which are not meeting Water Quality Standards and the reason why (for example, excess nutrients). To identify these lakes and streams in Michigan, we rely on recent, reliable water quality data. Our methods for determining whether a water body meets its WQS can be found in the Integrated Report. These methods are updated every two years in a process that involves review and comment by the public and USEPA. Please contact us if you or your group/agency has data that you would like included in this process. 

Who is responsible for developing TMDLs in Michigan?

EGLE's Water Resources Division is responsible for developing TMDLs.

How is a TMDL developed?

A TMDL is developed by determining the maximum daily load of a pollutant that a water body can assimilate and still meet Water Quality Standards. Generally, a TMDL begins by collecting and analyzing water quality data to determine the extent of the issue.  EGLE then identifies and determines the pollutant load from all point sources (discharges to surface waters that hold a National Pollutant Discharge Elimination System (NPDES) permit), and nonpoint sources (diffuse sources, such as land-applied manure from a small farm). To account for any uncertainty, a margin of safety is developed, and seasonal differences are also considered.

What is the role of Local Communities and Landowners in the development of TMDLs?

TMDL development is a public process that works best with the involvement of all affected parties. Participation by local communities, local government agencies (such as Health Departments), and landowners leads to improved TMDLs and ultimately better water quality.

What happens once a TMDL is developed?

Following development of a draft, a TMDL is noticed for public comment. After making any appropriate modifications in response to the public comment, the TMDL is sent to the United States Environmental Protection Agency for approval. Required pollutant load reductions from point source discharges in a TMDL watershed are implemented through existing programs, such as NPDES permits. Nonpoint sources of pollution are reduced mainly through voluntary programs and the work of local stakeholders. Work in TMDL watersheds can be funded by the Nonpoint Source program's grants. The efforts to clean-up nonpoint sources of pollution are often lead by local agencies such as conservation districts or watershed councils.


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