The ecological health condition of Guntersville Reservoir rated good in 2012. Guntersville’s ecological health scores have fluctuated within the good range all years except 2008 and 2010, when Guntersville rated fair. The fair ratings were largely because several ecological indicators (dissolved oxygen, chlorophyll and bottom life) at the forebay concurrently rated at the lower end of their historic ranges, which likely resulted from a dry weather pattern and low flow conditions during most of the summer months.
Ecological health scores tend to be lower in most Tennessee River reservoirs during years with lower flows because chlorophyll concentrations are typically higher and dissolved oxygen levels are lower. In turn, the low dissolved oxygen can negatively affect bottom life.
TVA monitors three locations on Guntersville Reservoir―the deep, still water near the dam called the forebay; the middle part of the reservoir; and the riverlike area at the extreme upper end of the reservoir called the inflow—usually on a two-year cycle.
Dissolved oxygen rated fair at the forebay and good at the mid-reservoir. This indicator has rated good each year at the mid-reservoir. At the forebay, however, low dissolved oxygen concentrations (<2 mg/L) periodically develop in a small area along the reservoir bottom during summer. This resulted in fair ratings some years and a poor rating in 2010.
Chlorophyll rated fair at the forebay and good at the mid-reservoir. Chlorophyll concentrations were elevated at the forebay during several sample periods. 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, when it rated fair.
The fish communities rated fair at all locations because the number of individuals and variety of species collected were slightly fewer than expected. Historically, ratings generally have fluctuated within the mid to upper end of the fair range at each location. However, the fish community rated poor (one point from fair) at the inflow in 2000. The inflow’s rating rebounded in subsequent years, possibly indicating that the poor rating was an anomaly.
Bottom life rated fair at the forebay and good at the mid-reservoir and inflow. Bottom life typically rates fair or good at all monitoring locations. The forebay received the only poor rating for this indicator. This occurred in 2010 because of reduced diversity and most of the organisms collected were those capable of tolerating poor water quality conditions.
Sediment quality rated fair at the forebay and mid-reservoir monitoring locations because PCBs were detected in the samples. 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 primarily to chlordane, which was detected in 1996, 2002 and 2004. PCBs were detected at this location in 2002.
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 Alabama Department of Public Health.