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Top 3 Impairments to Water Quality in the Basin

January 12, 2021
Photo: Chuck Sutherland

Water is ever-changing. And as it changes, so too does it shape and change its environment, our environment. When it comes to understanding the water quality of the Cumberland River basin, there are many factors to consider; from known activities impacting water quality, all the way down to the presence of tiny “bugs” that indicate water quality. The Cumberland River Compact prioritizes program and restoration work using the water quality data produced by the states of Tennessee and Kentucky.

Before we discuss some of the changes in water quality trends we have observed, we wanted to cover some of the basics as to where this data comes from. 

305(b)/303(d) Lists and the Clean Water Act

The water quality data that the Compact uses to inform our work comes from federally mandated lists called the 305(b) (all water quality) and 303(d) (impaired waters) lists. The names for these lists refer to sections 303(d) and 305(b) of the US EPA Clean Water Act. These sections of the Clean Water Act require states to evaluate the health of waters within their borders using available data and to determine if they meet water quality standards and designated uses. If they do meet the standards they are considered healthy. If they don’t, they are listed as impaired. 

These lists are great for many reasons:

  • They identify impacted streams and their watersheds that would benefit from Total Maximum Daily Load plans, 319 Clean Water Act grants, and/or other restoration efforts 
  • Teams of state and federal scientists are monitoring streams in every region of our 18,000 square mile basin. States are required to update these lists every 2 years  
  • Nearly 9,000 stream miles in the basin have been assessed!
  • Scientists monitor for a large number of causes (40+) and sources (60+) of water impairment to give the most accurate picture of possible reasons why a stream is unhealthy.
  • With this data, the public can have a greater understanding of water quality issues and how to help groups like the Cumberland River Compact address them

The availability of this data allows the Compact to see the big picture of what’s going on in the basin, and also where we will have the most success targeting our restoration efforts. To help our supporters better understand this data, we partnered with the Nature Conservancy in TN to create an interactive map called iCreek where you can explore the water quality of the basin — including learning what watershed you live in!

Processing water quality data from countless streams in order to produce these lists can be cumbersome, especially with the need to update the data every 2 years. There’s room for improvement when it comes to collecting water quality data and making it useful to the public, but what we do have is of significant value and provides great insight into the state of the waters in our Cumberland River basin.

Top Stream Impairments in the Basin

The Compact analyses the lists published by Tennessee and Kentucky to follow new trends in water quality that impact our work. These analyses help synthesize the data lists and collate the data from both states, which are often reported and published differently. 

The following are the top 10 listed impairments to water quality being fishable, drinkable, and/or swimmable in the Cumberland River basin: 

  • Pathogens ≈ 1,522 miles (16.9%)
  • Siltation ≈ 1,478 miles (16.5%)
  • Nutrients ≈ 1,002 miles (11.2%)
  • Altered Streamside Vegetation ≈ 753 miles (8.4%)
  • In-Stream Habitat Alteration ≈ 334 miles (3.7%)
  • Low Dissolved Oxygen ≈ 309 miles (3.4%)
  • Unknown ≈ 287 miles (3.2%)
  • pH ≈ 286 miles (3.2%)
  • Methylmercury ≈ 275 miles (3.1%)
  • Iron ≈ 166 miles (1.9%)
*percentages based on assessed stream miles in the basin, not total miles. 

Let’s take a closer look at the top three impairments. 


Pathogens’ presence indicates that water is contaminated by human or animal waste. Persons who come into contact with pathogens found in water can suffer headaches, diarrhea, cramps, nausea, or other gastrointestinal illness. Two common pathogens found in water are Giardia and Cryptosporidium. These parasites are the cause of two of the most common waterborne diseases in the U.S. Both can persist in the environment for months and are highly resistant to disinfection. Young children and people with compromised immune systems may be particularly at risk from pathogens. Certain species of fish and wildlife are unaffected by these microbes while other species experience symptoms similar to humans.

Pathogens can enter waterways by way of sewer overflows, leaking sewer lines, and polluted stormwater that washes bacteria from undisposed pet waste into the nearest stream. Pet waste that is left in the street, dog park, or even a person’s backyard contributes to major water quality problems in Nashville — scoop the poop! In agricultural areas, poorly chosen feeding, watering, and waste management locations can allow pathogens to make their way into our water. In rural settings, failing septic systems are often significant contributors to pathogen impairments.

In urban areas, high concentrations of pathogens are most often associated with heavy rainfall, which causes sewer system problems and carries pathogens from animal waste into our waterways.


Silt refers to the dirt, soil, or sediment that is carried and deposited by our water. While some silt in water is normal and healthy, many additional tons of silt find their way to our water every year, negatively impacting water quality. This pollution, known as siltation, results from erosion and land disturbing human activities, such as agriculture and construction.

Siltation negatively impacts ecosystems in many ways. Excessive silt clogs gills and smothers eggs and nests. It can bury the habitat aquatic insects need for survival, which impacts organisms up the food chain that eat these insects for survival. Siltation can also interfere with photosynthesis in aquatic plants resulting in a decrease in needed dissolved oxygen. Important components of aquatic habitat, which native aquatic species rely on for survival, are altered by siltation. These include the amount of light, the temperature, depth, and flow of water. In addition, pollutants like fertilizers, pathogens, pesticides, and heavy metals can be attached to soil particles that find their way to our water.

Siltation also increases levels of treatment needed for drinking water, fills up reservoirs and navigation channels, and increases a waterbodies likelihood of flooding.


The main sources of nutrient impairments are over-fertilized agricultural lands, as well as urban lawns and gardens. Other sources include livestock, pet waste, municipal wastewater systems. Farmers apply nutrients in the form of chemical fertilizers, manure, and sludge. When fertilizers exceed plant needs, are left out in the open, or are applied just before it rains, nutrients can wash into our waterways over land or seep into groundwater.

Many backyard fertilizers for gardens or lawns contain nutrients. Just like in a rural setting, excess fertilizer that is not taken up by plants can seep into groundwater sources or be carried by stormwater over land to streams and rivers. Most dishwashing detergents are another source of nutrients that can be traced back to the home. Finally, high concentrations of nutrients are also found in human and pet waste, which all too often contaminate our waters via leaking sewer lines or neglected pet waste.

These increased nutrient concentrations cause nuisance or toxic algae blooms in water bodies. These blooms can ruin swimming and boating opportunities, create foul taste and odor in drinking water, and kill fish and aquatic life by removing oxygen from the water. High concentrations of nutrients must be filtered from our drinking water since they can cause methemoglobinemia, a potentially fatal disease in infants, also known as blue baby syndrome.

Changes of Note

Pathogens, Siltation, and Nutrients are commonly our top three pollutants. But here are some trends and changes that we’ve noticed. 

  • Pathogen pollution jumped to the top of the list with the largest number of miles impaired, dropping siltation to the second most common pollutant. 
  • Methylmercury continues to be listed as the top impairments for the Lake Cumberland watershed in the headwater region of the Cumberland River basin. Methylmercury is a form of mercury that is highly toxic. Concerning amounts end up in waterways when coal is burned at local, regional, national, and international power plants. We see this as an emerging area of focus for our work that may require new approaches. In total, 61% of the streams assessed in this watershed are listed as impaired for one reason or another.
  • Many of our basin’s impairments are linked to urbanization, agriculture, and mining. So even if the specific impairments vary across the watershed, we know we can make a big impact on water quality by collaborating with partners in agriculture, urban centers, and mining communities. 

Data-Driven Restoration and Education for the Basin

The Cumberland River Compact serves each of the 14 watersheds that make up the Cumberland River basin, from Appalachia to the Ohio River. With the basin totaling over 18,000 square miles, it’s so important for us to have good data to prioritize restoration projects and education/outreach programs in areas that need it most. 

With 2021 bringing on new challenges and opportunities, we are working harder than ever to bring resources and expertise to both urban and rural areas of the Cumberland River basin. 

In urban areas, we know that planting trees and rain gardens, removing unused pavement, and installing innovative bioretention makes a difference in the health of our urban waters. In fact, this year the first bass in memory was caught on Richland Creek where the Compact removed a dam and renewed connectivity of the creek. 

In rural areas, we know that soil building agricultural Best Management Practices (BMPs), restoration of degraded streams, removal of dams, and youth and community education make a difference in the health of our rural waters. 

In 2021 we’re focused on working smarter with our talented staff to reach more areas of the basin with restoration and education resources. Some things you can look out for in 2021: 

  • River Friendly Farms Certification program 
  • DePave 
  • Restoration of Browns Creek 
  • Dam Removal and restoration on Stewart Creek in Smyrna
  • Expansion of minor bank restoration program
  • New Volunteer Leader program
  • Basin-wide Education Programming

Get Involved with the Compact

Now that you know some of the issues facing our Cumberland River basin waterways, how will you get involved?