Guntersville Reservoir

The ecological health of Guntersville Reservoir received a “good” rating in 2022, consistent with all years except 2008 and 2010, when Guntersville rated “fair”. The lower ratings were largely due to several ecological indicators (dissolved oxygen, chlorophyll, and bottom life) at the forebay concurrently rating at the lower end of their historic ranges, which likely resulted from the dry, low flow conditions during most of the summer months.

Dissolved oxygen and chlorophyll, the ecological indicators most responsive to changes in weather conditions, tend to rate lower during dry, low flow conditions, especially if periodic rain events wash nutrients and organic material into the reservoir. In turn, dissolved oxygen conditions along the reservoir bottom affect bottom life. Additional information about each indicator is provided in the paragraphs that follow.

The ecological health of Guntersville 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 three locations on Guntersville Reservoir—the deep, still water near the dam, called the forebay (Tennessee River Mile (TRM) 350.0); the middle part of the reservoir (TRM 375.2); and the river-like area at the extreme upper end of a reservoir, called the inflow (TRM 420.0 - 424.0)—usually on a two-year cycle. Only bottom life and the fish assemblage are assessed at the inflow monitoring location.

Guntersville 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 Guntersville Reservoir ‒ 2022

Dissolved oxygen

Dissolved oxygen in 2022 rated “good” at the two locations this indicator is monitored. Dissolved oxygen has rated “good” each year at the mid-reservoir. At the forebay, however, low dissolved oxygen concentrations (less than two milligrams per liter) sometimes develop in a small area along the reservoir bottom during summer. This resulted in “fair” ratings some years and a “poor” rating in 2010. Low flow conditions reduce mixing in the water column and can allow water to sit long enough that oxygen in the lower water column becomes depleted as it is used in the natural process of decomposition.

Chlorophyll

Chlorophyll in 2022 rated “fair” at the forebay and “good” at the mid-reservoir. Chlorophyll ratings have fluctuated between “good”, “fair” and “poor” at the forebay, generally in response to reservoir flows. Chlorophyll has rated “good” at the mid-reservoir each year except 1994 and 2007, when it rated “fair”. (The full complement of ecological indicators was not monitored in 2007.) 

Fish

The fish community in 2022 rated “fair” at the inflow and mid-reservoir locations, and “good” at the forebay. This aligns with historical ratings for the reservoir where scores have fluctuated within the “fair” range at the inflow and mid-reservoir locations, and between the mid-ranges of “fair” and “good” at the forebay. In 2022, the number and variety of fish observed at each location were consistent with long-term averages. A total of forty-six species were observed in 2022. Instances of disease and parasites were slightly elevated due to observations of fungus and parasites.

Bottom life

Bottom life in 2022 rated “good” at the inflow and “fair” at the mid-reservoir and forebay locations. Ratings typically vary between “good” and “fair” at each location. However, bottom life received a “poor” rating at the forebay location in 2010 because of reduced diversity, and most of the organisms collected were those capable of tolerating the lower dissolved oxygen concentrations that were observed along the reservoir bottom that year. 

Sediment

Sediment quality in 2022 rated “fair” at the forebay location where low concentrations of PCBs were detected and “good” at the mid-reservoir location where no PCBs or pesticides were detected and concentrations of metals were within suggested background levels.

Sediment quality commonly rates “fair” at the forebay due to one or more contaminants: PCBs, chlordane, or zinc. The sediment rating at the mid-reservoir has fluctuated between “good” and “fair” due to chlordane, which was detected in 1996, 2002 and 2004, and PCBs, which were detected at this location in 2002 and 2012.

Concentrations of chlordane and zinc have exhibited a trend of decreasing over the Ecological Health monitoring period. Chlordane was last detected at the forebay in 2002 and at the mid-reservoir in 2004. Zinc concentration has not exceeded suggested background levels since 2004 at either of the monitoring locations.

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 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 Guntersville Reservoir, visit the Tennessee Department of Environment and Conservation and the Alabama Department of Public Health web pages.