The ecological health of Wheeler Reservoir rated “fair” in 2017. Wheeler Reservoir rated either “good” or “fair” in all previous years except 2007 and 2011, when it rated “poor” both years. Generally, lower ecological health scores occur during years with lower flow. Low flow years typically result in higher chlorophyll concentrations and lower dissolved oxygen levels.
The ecological health of Wheeler 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 Wheeler Reservoir—the deep, still water near the dam, called the forebay (Tennessee River Mile (TRM) 277.0); the middle part of the reservoir (TRM 295.9); the Elk River embayment (Elk River Mile 6.0); and the river-like area at the extreme upper end of the reservoir, called the inflow (TRM 348.0)—usually on a two-year cycle. Only bottom life and the fish assemblage are assessed at the inflow monitoring location.
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>72 = Good
59-72 = Fair
<59 = Poor
|Elk River embayment||Poor||Poor||Good||Poor||Good|
Dissolved oxygen in 2017 rated “good” at the mid-reservoir location, “fair” at the forebay, and “poor” at the Elk River embayment. The lower ratings were due to low dissolved oxygen concentrations (<2 mg/L) in the lower water column during the summer. Dissolved oxygen has rated “good” at the mid-reservoir location in all previous years, but ratings have varied between “good”, “fair”, and “poor” at the forebay and embayment locations, primarily in response to reservoir flows.
In 2017, chlorophyll rated “good” at the mid-reservoir and “poor” at the forebay and Elk River embayment locations because concentrations were elevated in most of the samples collected. Elevated chlorophyll concentrations are common on Wheeler Reservoir. Chlorophyll typically rates “poor” at the forebay and Elk River embayment, but ratings have varied between “good”, ”fair”, and “poor” at the mid-reservoir location.
The fish assemblage in 2017 rated “good” at the four locations monitored. Historically, the fish assemblage has rated “good” at the forebay and in the “good” to “fair” range at the other monitoring locations. In 2017, the number and variety of fish observed at each location were consistent with long-term averages, and fish health was assessed a “good” rating with low incidences of disease and parasites. A total of fifty-one species was observed reservoir-wide. Top carnivores (e.g., largemouth bass), benthic invertivores (species that feed primarily on bottom-dwelling insects) and intolerant species (species known to require good water quality conditions) were well represented at each location. Some of the more interesting species observed included bowfin, stripetail darter, and orange-spotted sunfish.
Consistent with most previous years, bottom life in 2017 rated “poor” at the forebay and Elk River embayment monitoring locations and “good” at the mid-reservoir and inflow. The lower ratings were due to relatively low population densities, predominantly composed of benthic invertebrates able to tolerate the low dissolved oxygen concentrations that developed along the reservoir bottom during summer.
Sediment quality rated “good” at the forebay and Elk River embayment locations and “fair” at the mid-reservoir. “Good” ratings indicate no pesticides or PCBs were detected and the concentrations of metals were within suggested background levels. Low levels of PCBs were detected in the sediment sample collected at the mid-reservoir, resulting in a “fair” rating. Sediment quality generally rates “good” at the three locations monitored. However, PCBs have been detected in the sediments at each location in some previous years. DDT and chlordane also were detected in sediments at the mid-reservoir in 1994 and 2003, respectively.
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 Wheeler Reservoir, visit the Alabama Department of Public Health.