One of the key tools employed by the Clean Water Act (“CWA”) to help meet the statute’s goal of reducing pollution in the nation’s waters is the total maximum daily load (“TMDL”). A TMDL establishes the maximum amount of a particular pollutant allowed in a waterbody and serves as the jumping off point for further water quality restoration. The authority for developing a TMDL is found within the text of the CWA. Responsibilities for development and implementation of TMDLs are split between states and the EPA, however EPA may in some circumstances step in and develop a TMDL when the states have failed to do so. In other circumstances, EPA may chose to support collaborative efforts between states to implement pollution reduction efforts in multi-state watersheds. In the Chesapeake Bay watershed, a region that spans multiple states in the eastern United States, the EPA has developed a TMDL that those states must implement. That TMDL will govern how those states manage pollution discharges across a variety of industries including agriculture. Meanwhile, in the Illinois River watershed which includes Arkansas and Oklahoma, EPA is supporting collaborative pollution reduction efforts between the states, giving them more room to decide where pollution reductions come from.

What is a TMDL?

A TMDL is the maximum amount of pollutant allowed to enter a waterbody while still maintaining the water quality standards for that particular pollutant. Typically, one TMDL is developed for each pollutant that is threatening a waterbody, therefore a waterbody may have more than one TMDL in place at a time. While it is more common for a TMDL to address one specific pollutant, in some instances a single TMDL may be developed to address multiple pollutants in a waterbody or watershed.

In general, states are required to develop TMDLs and submit them to EPA for approval. Section 303(d) of the CWA directs states to create a maintain a list of impaired waters. For each water on the list, the state must identify which pollutants are responsible the impairment and then develop a TMDL aimed at restoring the waterbody. A TMDL should clearly identify the connection between the impairment of the waterbody, the causes of impairment, and the pollutant reductions needed to meet the relevant water quality standards. If EPA does not approve a state’s TMDL, then the agency will develop its own TMDL for the waterbody. Public participation is required during the TMDL development process, although the process for including the public varies from state to state.

After a TMDL is approved, it gets implemented through a combination of CWA permits and a variety of state, local, and federal programs. Both point and nonpoint sources of pollution will be affected by TMDL pollutant reduction requirements. Under the CWA, anyone who discharges a pollutant into a waterbody from a point source, an identifiable source such as a pipe or a ditch, requires a permit from EPA. Once a TMDL is established for a waterbody, point source permits will set pollutant limitations based on the TMDL. Pollution that enters a waterbody via nonpoint source pollution, such as agricultural runoff or eroding sediment, does not require a CWA permit. Therefore, state, local, and federal programs help to regulate pollution from nonpoint sources to meet the relevant TMDLs for a particular waterway.

Chesapeake Bay TMDL

The largest TMDL in the United States is the TMDL established for the Chesapeake Bay watershed. The Chesapeake Bay TMDL includes six states and the District of Columbia. EPA began developing the TMDL in 2007, finalized it in 2010, and requires significant reductions of nitrogen, phosphorus, and sediment in the Chesapeake Bay watershed by 2025. The pollution reductions will be met by targeting both point sources of pollution, and programs that will target pollution from nonpoint sources such as agricultural and urban runoff.

The Chesapeake Bay TMDL is the not the first attempt at a multi-state effort to reduce pollution in the Chesapeake Bay watershed. Prior to 2007, several of the states within the Bay watershed made multiple failed attempts to create pollution reduction agreements. Their failure to do so prompted EPA to use its authority under the CWA to develop the Chesapeake Bay TMDL.

Shortly after EPA issued the Chesapeake Bay TMDL was issued, a coalition of agricultural groups lead by the American Farm Bureau Federation (“AFBF”) filed suit, challenging EPA’s authority to implement the multi-state TMDL. In American Farm Bureau Fed’n v. U.S. Envtl. Prot. Agency, 792 F.3d 281 (3rd. Cir. 2015), the plaintiffs argued that while EPA had the authority to issue a TMDL, the authority to implement it fell to the states. According to the plaintiffs, EPA had improperly implemented the TMDL by setting pollutant discharge limitations for point and nonpoint sources to reach the overall pollution reduction goals. The plaintiffs argued that it was up to the states to decide how much pollution reduction would come from point sources and how much would come from nonpoint sources.

The court disagreed, concluding that not only did EPA have the authority to set overall limits for how much pollution could enter a waterway, it could also set limits for point and nonpoint source discharges. According to the court, setting such limits did not qualify as implementing the TMDL because it was still up to the states to determine exactly how the limits would be met. Although the plaintiffs appealed this decision to the United States Supreme Court, the appeal was not taken up. This means that the decision from the Third Circuit concluding that EPA can set limits for point and nonpoint source pollution within a TMDL is how the CWA is applied within the Third Circuit’s jurisdiction.

Currently, EPA is being sued by three of the states subject to the Chesapeake Bay TMDL and several plaintiffs groups for failing to hold New York and Pennsylvania to the standards set out in the TMDL. These lawsuits were filed in September, 2020, so it is currently unclear how the litigation will ultimately play out. To read more about these lawsuits, click here.

Illinois River Watershed

The Illinois River Watershed includes both Arkansas and Oklahoma. Both states have identified waterbodies within the watershed as impaired waters. Phosphorus and nutrient levels within the watershed are of particular concern for decades, and in 2003, Arkansas and Oklahoma entered a joint agreement to reduce pollution within the watershed.

Since 2003, the two states have entered additional agreements to conduct water quality studies and studies on the levels of phosphorus within the Illinois River watershed, partnering with EPA to develop scientific models that could be used to develop TMDLs. In 2018, EPA released the models for use to help Arkansas and Oklahoma evaluate further strategies for reducing phosphorus within the Illinois River watershed, including developing TMDLs. In 2020, the EPA granted additional funding to help support the continued collaboration between Arkansas and Oklahoma to reduce pollution in the watershed.

While no TMDL has been developed for the watershed, some believe that EPA should step in and create a TMDL like it did for the Chesapeake Bay. For the moment, EPA has invested in the collaborative effort between Arkansas and Oklahoma to reduce pollution in the watershed without a TMDL from the federal government.


TMDLs can have a large impact on agricultural operations. Any operation that requires a CWA permit on a waterbody with a TMDL will have that reflected in the permit it receives. Additionally, agricultural runoff is often targeted by TMDLs seeking to reduce nutrient pollution in impaired waterbodies. The Chesapeake Bay TMDL has been of great interest to the agricultural communities within the Bay’s watershed as pollution reduction programs have been implemented to achieve the goals of the TMDL. In the Illinois River watershed, the collaborative efforts from Arkansas and Oklahoma to reduce pollution have impacted agricultural operations. However, a TMDL would likely have a greater impact because the TMDL can set strict levels for discharge from point and nonpoint sources. Agricultural producers who require CWA permits could see stricter requirements for pollutant discharges, while those who produce agricultural runoff could also be subject to additional restrictions. The development of a TMDL for the Illinois River watershed is something that could affect many agricultural producers in the region.


To read the Chesapeake Bay TMDL, click here.

To read the court’s decision in American Farm Bureau Fed’n v. U.S. Envtl. Prot. Agency, click here.

To read the complaints recently filed against EPA concerning the Chesapeake Bay TMDL, click here and here.

For additional information on pollution reduction in the Illinois River watershed, click here.

To read the text of the CWA, click here.

For more National Agricultural Law Center information on the CWA, click here.