The ecological health of Fort Loudoun Reservoir rated “poor” in 2017. Ecological conditions in Fort Loudoun Reservoir were assessed a “poor” or low “fair” rating most years prior to 2017. Throughout the years, each ecological indicator at each location monitored has indicated some stress: high concentrations of chlorophyll, low dissolved oxygen concentrations, “fair” fish assemblage, “poor” bottom life, and elevated concentrations of metals and/or the presence of organic contaminants in the sediments.
The ecological health of Fort Loudoun 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 three locations on Fort Loudoun Reservoir: the deep, still water near the dam, called the forebay (Tennessee River Mile (TRM) 605.5); the middle part of the reservoir (TRM 624.6); and the river-like area at the extreme upper end of the reservoir, call the inflow (TRM 652.0). Only bottom life and the fish assemblage are assessed at the inflow monitoring location.
Fort Loudoun Reservoir was monitored annually from 1994 through 2007. After 2007, TVA began monitoring Fort Loudoun every other year.
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>72 = Good
59-72 = Fair
<59 = Poor
Dissolved oxygen rated “poor” at the forebay and “good” at the mid-reservoir. This indicator usually rates “good” at the mid-reservoir location, but ratings have varied between “good”, “fair”, and “poor” at the forebay, generally in response prevailing weather patterns and the related changes in reservoir flows. Poorer dissolved oxygen conditions typically occur as a result of reduced flows through the reservoir during dry conditions.
As part of TVA’s Reservoir Release Improvement Program in the late 1990s, TVA installed aeration equipment to add oxygen to the deep water above Fort Loudoun Dam and to improve conditions immediately downstream.
Chlorophyll concentrations in 2017 were elevated in most of the samples collected at both monitoring locations, resulting in “fair” ratings. Elevated chlorophyll concentrations are common on Fort Loudoun, typically rating “poor” or at the low end of the “fair” range. Exceptions have occurred at the mid-reservoir in years with higher flows such as 1993 and 2013. The higher flows reduced algal growth, resulting in improved (“good”) chlorophyll ratings.
The fish community rated “fair” at all three monitoring locations. Characteristics of the fish communities (e.g., fish abundance, species richness, and composition) were similar to long-term averages for the respective sampling locations. A moderate number of fish species were collected at each location, with a total of forty-one species observed reservoir-wide. The tolerant species, bluegill, gizzard shad and spotfin shiner, accounted for a significant portion of the fish collected at each location, but moderate numbers of fish intolerant to degraded conditions (brook silverside, black redhorse, and spotted sucker) also were observed. Lake sturgeon was observed at the mid-reservoir site and the inflow. Fish health was assessed a “good” rating with low incidences of disease and parasites.
Similar to previous years, bottom life rated “poor” at the forebay and inflow monitoring locations and “fair” at the mid-reservoir location. Typically, relatively few organisms are collected from the forebay and inflow locations, and those collected are primarily species able to tolerate a wide variety of environmental conditions. Bottom life at the mid-reservoir location typically rates “fair” due to greater diversity, which includes a better representation of intolerant species such as mayflies.
Sediment quality rated “good” at the forebay and mid-reservoir locations because no PCBs or pesticides were detected, and concentrations of metals were within expected background levels.
Problems with organic contaminants have persisted over the years as PCBs and chlordane are sometimes detected in the sediment samples from both monitoring locations. PCBs were last detected in the 2013 sediment samples. Chlordane, however, has not been detected in sediment samples since 2004. Additionally, elevated levels of zinc typically were present in the sediment samples up to 2002. Zinc naturally occurs in soils but can also originate from many sources. Zinc concentrations have exhibited a decreasing trend over the Ecological Health monitoring period (1990 – present).
TVA maintains a program to examine contaminants in fillets of fish collected from TVA reservoirs and their major tributary streams on a rotational basis. The data collected from this program are 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 Fort Loudoun Reservoir, visit the Tennessee Wildlife Resource Agency.