The Total Maximum Daily Load (TMDL) program, established under Section 303(d) of the Clean Water Act, focuses on identifying and restoring polluted rivers, streams, lakes, and other surface water bodies. A TMDL is a written, quantitative assessment of water quality problems in a water body and contributing sources of pollution. It specifies the amount a pollutant needs to be reduced to meet water quality standards (WQS), allocates pollutant load reductions, and provides the basis for taking actions needed to restore a water body. TMDLs are prepared for waters identified as impaired on the 303(d) list in the Integrated Report.

Additional information about TMDLs is available on the U.S. EPA TMDL website.

Ohio EPA's Watershed Approach

Ohio EPA organizes information about TMDLs and water quality monitoring by watersheds. A watershed is the area of land that drains into a lake or stream. Watersheds can be small - like the area that drains into the creek behind your house. Or, watersheds can be large - consider all the land, streams and rivers that drain into the Ohio River or Lake Erie.

The watersheds — or project areas — are shown in the map below. Click on the watershed labels to be taken to their respective pages for more information.

Multi-Watershed TMDLs

In the past, Ohio EPA has focused on developing TMDLs for specific watersheds or project areas, as outlined in the map above. After going around the state and completing surveys in all of its watersheds, it was noted many of the impairments were caused by similar sources. For that reason, Ohio EPA has decided to take a multi-watershed approach to address these impairments found in watersheds across the state. Multi-watershed projects are currently being developed for the following impairments: bacteria, sediment, habitat, nutrients, and AMDATs.

What's New

• Draft documents related to the TMDL process are available for review and comment on the Water Quality Programs page
• Study Plans
• Completed  Biological and Water Quality Reports
• Inland Lakes Sampling
• Map of Approved TMDLs as of July 2024
• List of U.S. EPA approved TMDLs as of October 2023

Guide to Total Maximum Daily Loads in Ohio

Guide to Total Maximum Daily Loads in Ohio (PDF)

What is a TMDL?

Total Maximum Daily Loads (TMDLs) are developed as a tool to help restore and protect waterbodies where beneficial uses are impaired or threatened for aquatic life, recreation, public drinking water, or human health. According to the Clean Water Act, states must develop TMDLs for all the waters identified on their Section 303(d) list of impaired waters, according to their priority ranking on that list.

The objective of a TMDL is to determine the loading capacity of a waterbody and to allocate the load among different pollutant sources. A TMDL identifies the links between the waterbody use impairment, sources of impairment and the pollutant load reductions needed to meet the applicable water quality standards.   It serves as a roadmap for measures that can be taken to improve water quality.

Under the TMDL, sources of pollutants are classified as either point sources, which receive a waste load allocation (WLA), or nonpoint sources, which receive a load allocation (LA). Point sources include all sources subject to regulation under the National Pollutant Discharge Elimination System (NPDES) program, including but not limited to wastewater treatment facilities and municipal separate storm sewer systems (MS4s). Nonpoint sources include all remaining sources of a pollutant as well as natural background loads. In addition to accounting for seasonal variations in water quality, a margin of safety (MOS) will be calculated to account for uncertainty in predicting how well pollutant reductions will result in meeting water quality standards. An allowance for future growth (AFG) can be included to account for anticipated new or increased pollutant loadings.

Nonpoint source load reduction actions under a TMDL involve collaboration between local, state, and federal partners and can include non-regulatory and incentive-based (e.g., a cost-share) programs. In addition, waterbody restoration can be assisted by voluntary actions on the part of citizen and/or environmental groups.

Basic Steps of the TMDL Process

TMDLs and Regulatory Authority

Preparing a TMDL does not give Ohio EPA additional regulatory authority over nonpoint sources of pollution that are targeted for load reduction under the TMDL. The TMDL contains “reasonable assurances” that load reductions from nonpoint sources can be accomplished, but this normally involves pointing to things like activities that are supported through various grant programs and other efforts, including voluntary measures, that reside outside of Ohio EPA.

Collaborative Implementation Strategies

There is flexibility to adjust the implementation strategies under the TMDL to align with other state water quality plans, such as H2Ohio. While U.S. EPA is involved in reviewing state TMDL plans, states take a lead role in crafting and implementing the strategies within the TMDL to meet the pollutant reduction and water quality improvement goals. As part of the TMDL process, Ohio EPA would work in collaboration with key stakeholders at the local, state, and federal level in developing actions, measures, and timelines for meeting the goals in the TMDL. Using principles of adaptive management, the State works with partners to identify successes and continuously assess and adjust strategies needed for pollutant reductions and water quality improvements. 

Public Involvement in the TMDL Process

Ohio has a robust five-step public involvement process for its TMDL program.  These requirements are found in Ohio Revised Code (ORC) Section 6111.562 and allow for public participation in four key stages of TMDL development process

1. the project assessment study plan;
2. the biological and water quality report;
3. the loading analysis plan;
4. the preliminary modeling results.  

There is also opportunity for public comment and review on the official draft of the TMDL under ORC Section 6111.563.  Stakeholders will be notified and asked to review and comment on each of the five steps. Each document through the preliminary TMDL modeling results will have a minimum 30-day comment period; the official draft TMDL receives a 60-day comment period.  

How do I stay informed?

Ohio EPA sends announcements about the TMDL, its findings and associated public meetings to local newspapers and to those who express an interest. To be added to the list for updates, subscribe to Ohio EPA’s TMDL listservs at: https://public.govdelivery.com/accounts/OHEPA/subscriber/new

Implementation

The individual watershed pages on the website contain information on TMDL implementation projects that have been funded through Ohio EPA's Nonpoint Source Pollution grants program. The listed projects are not all inclusive. For more information regarding projects funded through these grant programs, see the following links:

• Section 319 Grants
• Great Lakes Restoration Initiative Grants

TMDL Project Contacts 

Please direct all questions and comments regarding TMDL projects to our email, EPATMDL@epa.ohio.gov