The ecological health of Nickajack Reservoir scored at the upper end of the fair range in 2012. Historically, ecological health scores have fluctuated within the good range. The lower rating in 2012 was the result of two ecological indicators—chlorophyll and sediment quality—scoring at the lower end of their historic ranges.
Nickajack has consistently scored among the highest of all the reservoirs monitored by TVA. Nickajack is a small, narrow reservoir with a short retention time. It usually takes only three or four days for water to flow through the reservoir, which helps keep the water mixed, preventing it from stratifying (separating into layers of different temperatures) during the summer. This allows oxygen in the lower water column to be replenished and limits algal growth, thereby reducing chlorophyll concentrations.
As in previous years, dissolved oxygen rated good at the forebay.
Chlorophyll rated poor. Chlorophyll has rated good most years. However, dry conditions and resultant low flows through the reservoir in 2007 and 2012 allowed more time for algae to grow, resulting in poor ratings.
The fish community rated fair at the forebay and good at the inflow. Consistent with previous years, fewer fish and fish species were collected at the forebay than expected and a greater proportion of those were tolerant individuals. The fish community has rated good at the inflow all years except 2011, when it scored one point below the good range.
As in most previous years, bottom life rated good at both monitoring locations. Typically a “good” variety of organisms are found, including long-lived and sensitive organisms — such as snails and mayflies — which are indicative of good water quality and conditions that allow for long-term survival.
Sediment quality rated fair due to low levels of PCBs. No pesticides were detected, and concentrations of metals were within expected background levels. Low levels of PCBs have been detected in some previous years, and chlordane was detected in 1993.
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 Nickajack Reservoir, visit the Tennessee Wildlife Resource Agency.