Watts Bar Reservoir

The overall ecological health condition for Watts Bar Reservoir rated “fair” in 2022. Ecological health scores for Watts Bar typically have fluctuated between the upper end of the “fair” range and “poor”. The one exception is 2020, when the reservoir received a “good” rating. Ratings for Watts Bar Reservoir have fluctuated in a pattern that generally follows reservoir flow conditions. The indicators most responsive to flow are dissolved oxygen and chlorophyll, which typically receive lower ratings during dry, low flow years.

The ecological health of Watts Bar Reservoir has been monitored using the same methodology since 1994 — usually on a two-year cycle. Ecological health evaluations focus on five indicators: dissolved oxygen, chlorophyll, sediment quality, benthic macroinvertebrate community (bottom life), and the fish assemblage. Monitoring takes place at four stations on Watts Bar Reservoir — the deep, still water near the dam, called the forebay (Tennessee River Mile 532.5); the middle part of the reservoir (Tennessee River Mile 560.8); and the riverlike areas at the extreme upper end of the reservoir in the Tennessee (miles 600 to 601) and Clinch (miles 19 to 22) Rivers, called inflows. Each ecological indicator is monitored at the forebay and mid-reservoir locations. Only bottom life and the fish assemblage are assessed at the inflow locations.

Watts Bar Reservoir Ecological Health Ratings, 1994-2022

To view or export the data, click on the menu in the top-right corner of the chart.

 >72 = Good

 59-72 = Fair

 <59 = Poor

Ecological Health Indicators for Watts Bar Reservoir ‒ 2022

Dissolved oxygen

Dissolved oxygen in 2022 rated “poor” at the forebay and “good” at the mid-reservoir monitoring location. Dissolved oxygen has rated “good” at the mid-reservoir all years monitored except 2008 and 2010, when it rated “fair” and “poor”, respectively. Low dissolved oxygen levels (<2 mg/l) have developed in a portion of the lower water column for a short period at the mid-reservoir during several years. However, the area affected was larger in 2010 than in other years, resulting in the only “poor” rating for this indicator at this location. Ratings have varied between “good”, “fair”, and “poor” at the forebay.  

Prevailing weather patterns and the related changes in reservoir flows are major factors in differing dissolved oxygen conditions from year to year. Poorer dissolved oxygen conditions typically occur as a result of reduced flows through the reservoir during dry conditions. As part of TVA’s Reservoir Release Improvement Program in the late 1990s, TVA installed aeration equipment at Watts Bar Dam to improve the quality of water released from the dam. Learn more about these improvements here.

Chlorophyll

Chlorophyll in 2022 rated “poor” at the forebay and “fair” at the mid-reservoir monitoring location. This is consistent with most previous years; however, summer average chlorophyll concentrations have fluctuated through time, resulting in “fair” and “poor” ratings at both locations. Similar to dissolved oxygen, weather conditions, particularly the timing and amount of rainfall, and the related changes in runoff are major factors in the variation observed from year to year.

Fish

The fish community rated “good” at the four locations this indicator is monitored. Historically, the fish community has rated “good” at the Tennessee River inflow and in the “good to fair” range at the other monitoring locations. In 2022, the diversity (number of species) and abundance of fish observed at each location were consistent with historical samples. A total of forty-three species was observed in 2022. Fish health was assessed a “good” rating with low incidences of disease and parasites.

Bottom life

Bottom life in 2022 rated “good” at the mid-reservoir, “fair” at the Tennessee and Clinch inflow locations, and “poor” at the forebay. The ratings in 2022 were similar to those of recent years at each monitoring location except the Tennessee River inflow. Historically, the Tennessee inflow has routinely received a “poor” rating due in part to the difficulty of obtaining samples of substrate. Substrate conditions suggested that this sample reach had been scoured and was likely composed mostly of bedrock, which is not conducive to many organisms. In 2016, the Tennessee River inflow monitoring location was moved approximately one mile upstream from its previous location and has since rated “fair” three of the last four sampling years. 

Bottom life at the forebay generally is assessed scores at the low end of the “fair” range or “poor” due to the limited number and variety of organisms collected. At the forebay, a limiting factor is the low dissolved oxygen conditions that develop in the lower water column each year.

Sediment

Sediment quality rated “good” at the two locations this indicator is monitored: the forebay and mid-reservoir. No PCBs or pesticides were detected, and concentrations of metals were within suggested background levels.  

Sediment quality commonly rates “fair” at both locations due to one or more contaminants: typically, PCBs, chlordane and/or arsenic. Arsenic occurs naturally in the soils but can also originate from other sources. Arsenic concentrations in sediments deposited in the reservoir are generally near – slightly above or below – suggested background concentrations. The pesticide chlordane was detected in some sediment samples collected from Watts Bar Reservoir in the 1990’s and early 2000’s. This pesticide was banned from use in the 1980s but continues to be detected sporadically in sediments because of its persistence in the environment. Similarly, PCBs were banned from commercial production in 1979, though they may be present in products and materials produced before the ban. PCB concentrations have, however, declined in fish samples collected from Watts Bar Reservoir. 

Fish consumption advisories

TVA maintains a program to examine contaminants in fish fillets from TVA reservoirs and their major tributary streams on a rotational basis. The data collected from this program are distributed to the state officials who are responsible for placing or removing fish tissue consumption advisories on those bodies of water. For information on advisories currently in effect for Watts Bar Reservoir, visit the Tennessee Department of Environment and Conservation web page.