Nutrient Pollution

Restoring the Harpeth

The Harpeth River is impaired and does not meet state water quality standards.  In fact, at pollution levels prevailing over the past several years, the Harpeth River is already past a tipping point for the production of harmful algae blooms.

A pollution reduction plan is in the works for the Harpeth River, and you can help!

  • ADD YOURSELF to the Tennessee Department of Environment & Conservation (TDEC) Harpeth River TMDL email distribution list so you can stay up to date on the process of establishing a pollution reduction study and plan.
  • CONTACT US here at the Harpeth Conservancy if you are interested in joining a stakeholder group to help develop a successful pollution reduction plan for the Harpeth River and/or if you want to receive email updates.
  • BECOME A CITIZEN SCIENTIST by downloading the free Water Reporter app and documenting problems you see on the Harpeth River.
  • LEARN MORE about TMDLs in general, the Harpeth River TMDL specifically, and other stakeholder-led TMDLs across the country below.

The Problem

The Harpeth River is polluted. It is on Tennessee’s list of impaired waters because the conditions of the river violate state water quality standards. A primary concern is high levels of phosphorus, a nutrient that can cause excessive algae growth (including toxic blue-green algae), deplete dissolved oxygen stores in the water, harm or kill aquatic life, and potentially poison the community water supplies. 

Polluting the water with phosphorus can trigger cultural eutrophication, where artificially elevated nutrients cause runaway plant and algae growth. Excessive nutrients act on algae in streams the same way fertilizer acts on your grass lawn, by increasing the growth rate and size. Thick algal blooms can block the sunlight from penetrating the surface of the water, which starves the plants growing on the riverbed. When the excessive algae dies and decomposes, it robs the water of oxygen, creating a “dead zone” that suffocates fish and other aquatic animals.

Worst of all, excessive nutrients can trigger a bloom of cyanobacteria (also known as blue-green algae), which can be toxic and dangerous to aquatic life and humans. The toxins produced by blue-green algae have been linked to gastrointestinal diseases, neurological diseases like Parkinson’s and Alzheimer’s, liver failure, and even death. CLICK HERE for more information about the dangers of blue-green algae.

The Response

The Tennessee Department of Environment & Conservation (TDEC) is the lead agency for an effort to study the Harpeth River watershed, establish pollution limits needed to meet water quality standards, and implement those limits successfully. To that end, TDEC has begun the process of developing a pollution reduction study and plan, called Total Maximum Daily Load (TMDL) to restore the Harpeth River.  


303(d) List: Under Section 303(d) of the Clean Water Act, all states must maintain a list of water bodies that fail to meet water quality standards and update the list every two years. The “303(d) List” identifies a state’s impaired waters so the sources of impairment can be described and corrective actions can be taken. Once a river is on the 303(d) List, it can only be delisted if the river was listed accidentally in the first place or it achieves applicable water quality standards. The Harpeth River has been listed as impaired by phosphorus pollution since 2004 (and for nutrients since 1996), leaving little doubt that the listing was not in error and the river is not on track to achieve water quality standards based on current practices.   

TMDL: A TMDL is the maximum amount of a pollutant that a waterbody can receive and still meet state water quality standards, including allocations of specific limits to each of the pollutant’s sources – “waste load allocations” for point sources (e.g. sewer treatment plant discharges) and “load allocations” for nonpoint sources (e.g. agricultural runoff). The calculated TMDL must also factor in a margin of safety and consideration of seasonal variation and critical conditions. The term “TMDL” is used to refer both to the limits set for a pollutant in a river body and to the study conducted to determine those limits. 

WLA: Waste load allocations (WLAs) are limits to point sources of pollution, such as wastewater treatment plant discharges. Implementation is relatively straightforward. Point sources that discharge to waters of the United States are regulated by National Pollutant Discharge Elimination System (NPDES) permits, so implementing a WLA tends to be done through NPDES permits. The City of Franklin, for example, has a sewage treatment plant that discharges large amounts of phosphorus into the Harpeth River but (usually) operates within the limits of its NPDES permit. The Harpeth TMDL may result in a WLA that forces Franklin’s sewage treatment plant to obtain an updated NPDES permit with a more stringent phosphorus limit.

LA: Load allocations (LAs) are limits to nonpoint sources of pollution, such as agricultural runoff and unregulated stormwater. Unlike point sources, there is no direct regulatory control over nonpoint sources. Implementing LAs relies on voluntary landowner participation in best management practices (BMPs) to limit nonpoint pollutant discharges into the impaired water. Because LAs do not have the regulatory backing of NPDES permits, compliance cannot be presumed and the EPA instructs that a TMDL should provide “reasonable assurances that nonpoint source control measures will achieve the expected [pollutant] load reductions.” CLICK HERE to learn more about reasonable assurances in the context of the Chesapeake Bay TMDL.

TMDL Development process

Typically, TMDLs are done in five steps: ​

First, the river is identified as impaired on the state’s 303(d) list.

Second, the state water quality and NPDES permitting agency (here TDEC) initiates a study to determine the sources of impairing pollutant(s) and potential remedies.

Third, the agency publishes a draft TMDL, receives public comment on the draft, and submits a revised draft to the EPA for approval. The TMDL allocates WLAs and LAs (along with a margin of safety and seasonal variation) to restore the impaired river to state water quality standards.


Virginia DEQ graphic - TMDL Development Process

Fourth, an implementation plan helps to organize continued water quality improvement efforts, especially voluntary landowner measures to achieve LAs and incentives therefor.

Finally, ongoing efforts to monitor and maintain water quality ensure than the TMDL was successful in getting the river delisted and that there is no significant backsliding, or else the process starts again.

Monitoring water quality is critical throughout the process. TDEC uses data collected from monitoring efforts to compose the 303(d) List of impaired waters, and monitoring is necessary to ensure the post-implementation efficacy of a TMDL in restoring the water. Anyone can participate in collecting water quality data; there are several parties contributing monitoring data to the Harpeth River TMDL. 

You can help collect valuable monitoring data on the Harpeth River! CLICK HERE to learn more about becoming a Harpeth Conservancy citizen scientist and using the Water Reporter app to document issues you see on the Harpeth, such as algae blooms and construction silt runoff.

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