Dr. Brett Hartis, Program Manager for Aquatic Plants for TVA answers questions from Janice Moody-Vice President of WBLA

Janice Moody: What percentage of Watts Bar Lake is now covered with invasive weeds? We understand that TVA has not updated their “grey scale map” since October 2015.What is your best estimate or educated guess? TVA indicated in 2015 that 5 percent of the shoreline was impacted. I think you or someone equated that to 400 acres. You mentioned in our February 6th meeting that coverage may have tripled last year, so could it be 1200 acres? Would this work out to be 3 percent coverage of the entire lake. Or is that percentage much higher?

Dr.Brett Hartis: This would be a tough one given that imagery hasn’t yet been updated so, as you mentioned, we haven’t been able to update a map as of yet. Just an unofficial guess, I would say that we have gone from approximately 200 acres (in 2015) to maybe 3 to 4 times that (600-800 acres) this past year. The 5 percent estimate was based on linear residential and commercial shoreline that was impacted at the time (mostly located around thiefneck and south). Percent coverage will come once we are able to update the grey scale map, which we are waiting on updated imagery from google to calculate.

Janice Moody: If the aquatic plants/weeds increases continues at the present rate, when will we reach 20%? Of the shoreline or the entire lake? At 20% how much (acres) shoreline shallows will be covered with weeds?

Dr.Brett Hartis: This is all going to be relative to the amount of “littoral” habitat present in the lake. Watts Bar does have large expanses of shallow water in places, but even if all of that habitat was inhabited by plants, it still wouldn’t equate to more than 30 or 40% at my best guess. For example, Guntersville has aquatic plants growing in nearly every place that they can possibly grow, and they are closer to 40% of the entire lake.

Janice Moody: Is anyone at TWRA doing research on the various chemical, biological and mechanical control methods? I understand mechanical control is probably not as feasible on Watts Bar Lake because of the rocks and stumps. We understand that mechanical harvesting does not remove the weeds to the lake bottom, they just cut a swath out of the weed beds at varying depths. Mechanical harvesting may not a good solution for Watts Bar Lake and its expensive.

Dr.Brett Hartis: I am not aware of any research being done by TWRA, but there have been literal decades of research done on aquatic plant management methods. Have a look at the Aquatic Plant Management Society, a group I have been associated with for years. They are the authority on aquatic plant management research.

Janice Moody: How many acres on Watts Bar Lake are less than 25’ deep?

Dr. Brett Hartis: That is a tough one to guess, mainly because bathymetric (depth) data for the lake is normally as old as the lake itself and not digitized (paper copies only). I have digitized a few lakes in my day and at about 2 weeks or more per lake, it is quite the task. I will speak with river operations to see what is available but last I checked, no one had digitized specific depths.

Janice Moody: Could you tell us where TVA is planning to treat on Watts Bar Lake in 2017? Has that decision been finalized? How is the decision made as to where TVA treats?

Dr.Brett Hartis: We currently have several dozen sites going through our own internal environmental reviews to be treated in 2017. Not all of these will make the cut, but most should. Once we have this finalized, I will send out a list. These sites were basically determined by me during the surveys this year. I included any public access area which did, or has the potential to grow aquatic plants. As always, if we are made aware of new sites or sites that we aren’t currently managing, we will check to make sure they are developed and public, and work them through our internal and external review process.

Janice Moody: What other questions should we be asking you?

Dr.Brett Hartis: That’s a good question in itself. I am here whenever they are thought of to answer them the best I can.

Janice Moody: Will TVA conduct a survey (update grey scale map) in 2017?

Dr.Brett Hartis: We will complete a survey in 2017 similar to what we did in 2016 to determine distribution of hydrilla in a general sense. Like this year, we are at the mercy of having up to date imagery in order to get an exact number (like we got in 2015). Basically, our on the ground surveys are to determine what species are where, and we use satellite imagery and aerial photography to fill in the blanks and get good estimates on actual totals.