Nickajack Reservoir

The ecological health of Nickajack Reservoir received a “good” rating in 2022. Historically, ecological health scores have fluctuated within the good range except in 2012, when the reservoir received a “fair” rating. 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.

The ecological health of Nickajack 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 two locations on Nickajack Reservoir — the deep, still water near the dam, called the forebay (Tennessee River Mile 425.5) and the river-like area at the extreme upper end of a reservoir, called the inflow (Tennessee River Mile 469 to 470). Only bottom life and the fish assemblage are assessed at the inflow monitoring location.  

Nickajack 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 Nickajack Reservoir - 2022

Dissolved oxygen

As in previous years, dissolved oxygen rated “good” at the forebay in 2022. 

Chlorophyll

Chlorophyll rated “good” in 2022. Chlorophyll has rated “good” most years. However, dry conditions and the resultant low flows through the reservoir in 2007 and 2012 allowed more time for algae to grow, resulting in “poor” ratings.

Fish

Consistent with previous years, the fish community in 2022 rated “fair” at the forebay and “good” at the inflow. Though fish abundance was observed at historic highs at the forebay monitoring location, the composition primarily consisted of tolerant species, while top carnivores, benthic invertivores, and intolerant species (species known to require good water quality conditions) were well represented at the inflow location. A total of forty-one species were observed in 2022, and fish health was assessed a “good” rating with low instances of disease and parasites at both locations.

Bottom life

Bottom life in 2022 rated “good” at the inflow and “fair” at the forebay location. Historically, the forebay location has predominately rated “good”; however, scores have fluctuated, resulting in “fair” ratings in 2007, 2011, and 2022.  The inflow location has received “good” ratings since monitoring began.  Typically, a “good” variety of organisms are found at both locations, 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

Sediment quality rated “good” in 2022. No PCBs or pesticides were detected, and concentrations of metals were within suggested background levels. Sediment quality has increasingly rated “good”. Prior to 2014, ratings fluctuated between “good” and “fair” due to detection of low levels of PCBs. PCBs were banned from commercial production in 1979, though they may be present in products and materials produced before the ban.

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 Nickajack Reservoir, visit the Tennessee Department of Environment and Conservation.