The overall ecological health condition for Watts Bar Reservoir rated “fair” in 2018. Ecological health scores for Watts Bar have fluctuated between the upper end of the “fair” range and “poor” and have generally followed 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. Ecological health evaluations focus on five indicators: dissolved oxygen, chlorophyll, sediment quality, benthic macroinvertebrate community (bottom life), and the fish assemblage. TVA monitors four locations 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—usually on a two-year cycle.
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>72 = Good
59-72 = Fair
<59 = Poor
|Tennessee River inflow||–||–||Good||Poor||–|
|Clinch River inflow||–||–||Good||Fair||–|
Dissolved oxygen rated “fair” 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 during summer 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 rated “fair” at the forebay and mid-reservoir monitoring locations. 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.
The fish assemblage rated “fair” at the forebay and “good” at the mid-reservoir and both inflow monitoring locations. Historically, the fish assemblage at all four locations has rated in the “fair to good” range. In 2018, the diversity and abundance of fish observed at each location were consistent with long-term averages. A total of forty-seven different species was observed reservoir-wide. Overall, fish composition was dominated by a few species such as bluegill, gizzard shad, bluntnose minnow, and spotfin shiner. Black redhorse (a species generally intolerant of poor water quality) also were present in high numbers at the Clinch River inflow monitoring location. Fish health was assessed a “good” rating with low incidences of disease and parasites.
Bottom life rated “fair” at the forebay and Clinch inflow, “good” at the mid-reservoir, and “poor” at the Tennessee inflow. Scores for bottom life in 2018 were similar to those of recent years at each monitoring location except the Tennessee River inflow. In prior sampling years, “poor” ratings became common for the Tennessee inflow 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 the bottom life obtained a “fair” rating. In 2018, this location rated “poor”. A variety of organisms was collected (mussels, clams, snails, and caddisflies) but in very low numbers. The limiting factor is likely the substrate, which was composed mostly of gravel and sand. In this high-velocity river reach, these substrates likely are shifting.
Bottom life at the forebay generally is assessed scores at the low end of the “fair” range or “poor” due to the limited numbers 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 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.
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 is 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 Wildlife Resource Agency.