The ecological health condition of South Holston Reservoir rated “fair” in 2021. Historically, ecological health ratings have fluctuated within the “fair” and “poor” range. In all years monitored, low ratings for two indicators — dissolved oxygen and bottom life — consistently reduce the reservoir’s overall health score. In 2021 and other years in which South Holston rated fair, several indicators scored at the upper end of their historical ranges.
The ecological health of South Holston 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 fish assemblage. TVA monitors two locations on South Holston Reservoir — the deep, still water near the dam, called the forebay (South Holston River Mile 51.0), and the middle part of the reservoir, called the mid-reservoir (South Holston River Mile 62.5).
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>72 = Good
59-72 = Fair
<59 = Poor
*Sediment quality was assessed based on monitoring results from 1994 through 2018.
As in previous years, dissolved oxygen rated “poor” at both monitoring locations. Both locations experienced low dissolved oxygen concentrations (<2 mg/L) in portions of the lower water column during summer and autumn. Low dissolved oxygen concentrations are not uncommon in the lower water column of deep, tributary reservoirs with long residence times (time that water spends in the reservoir). Although oxygen concentrations in the upper water column remain adequate for aquatic life, the animals that live on or in the sediments can be exposed to low concentrations.
Chlorophyll rated “good” at the forebay and “fair” at the mid-reservoir. Chlorophyll has rated “good” at the forebay in all years except 1994, when it rated “fair” due to lower-than-expected concentrations. Chlorophyll ratings have varied between “good” and “fair” at the mid-reservoir location.
The fish community in 2021 rated “good” at both monitoring locations. Characteristics of the fish communities (e.g., fish abundance, species richness and composition) were similar to long-term averages for the respective sampling locations. Smallmouth bass and walleye were the most abundant top carnivores at both locations. Bluegill and spotfin shiners were the predominant forage fish. A total of twenty-eight species were observed in 2021. A golden shiner and a goldfish were collected at the forebay. This is the first time these species have been collected on South Holston Reservoir. Fish health was assessed a “good” rating with low incidences of disease and parasites.
Bottom life in 2021 rated “fair” at the forebay and “poor” at the mid-reservoir location. Historically, bottom life has rated “fair” or “poor” at both locations because relatively few organisms were found in the samples, and most are species able to tolerate a wide range of conditions.
Sediment samples were not collected from South Holston Reservoir in 2021. Sediment quality was assessed a “good” rating at both locations based on monitoring results from 1994 through 2018. In 2012, 2015, and 2018, sediment quality rated “good” at both monitoring locations because no PCBs or pesticides were detected in the sediment samples, and the concentrations of metals were within suggested background levels. Historically, sediment ratings have fluctuated between “good” and “fair” at both locations dependent on whether chlordane was detected. Chlordane, a pesticide previously used to control termites and crop pests, was last detected in the sediments of South Holston Reservoir in 2002. Sediment quality also rated “fair” at the forebay in 2008 because the concentration of arsenic was slightly above expected background levels.
TVA maintains a program to examine contaminants in fillets of fish collected 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 South Holston Reservoir, visit the Tennessee Wildlife Resource Agency.