Reservoir Health Ratings

TVA values clean water, and using rigorous criteria, it monitors the health of its reservoirs to best understand how to intervene when necessary to boost water quality.

Want to know how clean your reservoir is? Check it here. TVA monitors ecological conditions at 69 sites on its 31 reservoirs on a two-year cycle (more often if ecological conditions merit).

The health ratings are based on five factors:

  1. Dissolved Oxygen. A good rating means there’s plenty of oxygen to support fish and other aquatic life.
  2. Chlorophyll. A measure of algae in the water, a good rating means that algal growth is within the expected range. If levels are too low, the reservoir’s food web can be affected; if levels are too high, water treatment costs may increase and oxygen levels in the bottom layer of water may suffer from decaying algae.
  3. Fish. A good rating means there are a large number and good variety of our finned friends.
  4. Bottom dwellers. A good rating means that there are plenty of worms, insects and snails thriving on the reservoir floor.
  5. Sediment. A good rating means sediment is free from PCBs, pesticides and large concentrations of metals.

When monitoring the water, TVA takes samples from up to four locations, depending on the reservoir’s size. These are:

  1. Forebay: The deep, still water near a dam.
  2. Mid-reservoir: This is where the transition occurs from a river-like environment to a lake-like one.
  3. Embayment: A large slough or cove. (TVA monitors only four of these: Hiwassee River on Chickamauga Reservoir, Big Sandy River on Kentucky, Bear Creek on Pickwick and Elk River on Wheeler.)
  4. Inflow: The river-like area at the extreme area at the extreme upper end of a reservoir.

Stream Ecological Health

TVA Watershed Offices, staffed by water-resource professionals and education specialists, work throughout the Tennessee Valley to improve water-resource conditions. They utilize data collected at more than 100 sites each year to help identify key issues and potential improvement projects.

Fish Consumption Advisories

State agencies are responsible for advising the public of health risks from eating contaminated fish. Each state uses its own criteria for deciding whether an advisory is necessary. TVA assists the states by collecting fish from TVA reservoirs and checking the tissue for metals, pesticides, PCBs and other chemicals that could affect human health. Check the fishing regulations published by your state for specific advice on fish consumption (available wherever fishing licenses are sold).

Two national advisories related to mercury in fish are also in effect. In January 2001, the Environmental Protection Agency (EPA) advised pregnant women, nursing mothers and young children to limit fish consumption to one meal per week. EPA’s advice is for freshwater fish caught by friends and family from local waters. The Food and Drug Administration issued a companion advisory for the same groups of people recommending against consumption of shark, swordfish, king mackerel and tilefish purchased in stores and restaurants.

Chemicals Responsible for These Advisories

Five chemicals—PCBs, chlordane, DDT, dioxins and mercury—are primarily responsible for contaminating fish in the Tennessee River system.

PCBs, chlordane and DDT are no longer manufactured because they have been linked to a variety of health concerns. PCBs were used in many products, from electrical transformers to hydraulic fluid for farm equipment. Chlordane was used mostly to control termites, and DDT was used to control mosquitoes, flies, boll weevils and many other insects.

Dioxins have also been linked to a variety of health concerns. They are unintended by-products of the industrial processes used to make white paper products and some herbicides. The incomplete combustion of certain inorganic materials, like plastics, also produces dioxins.

Too much mercury in the diet can cause brain and kidney damage in humans. The presence of mercury in reservoirs and streams is usually due to past industrial activities, and levels of the substance have declined as industries have stopped discharging their wastes into waterways.

These five chemicals do not dissolve well in water, so they are found mostly in the mud on the bottom of reservoirs and rivers. They can build up in the fatty tissue of fish, particularly bottom feeders.

Reducing Health Risks

If you eat fish often, there are ways to significantly reduce your risk from pollutants. Eat smaller, younger fish. Discard the skin and fatty part of fish fillets, and broil, bake or grill your fish. It’s also a good idea to vary the kinds of fish you eat. Substitute a few meals of crappie, sunfish and perch for fish that tend to accumulate contaminants more rapidly. Bottom-dwelling fish like catfish and carp, for example, tend to accumulate more PCBs and other organic pollutants, and large predators such as bass tend to accumulate more mercury.