“It started, we think, around Cherokee boat ramp,” said Scott Hyatt, the operations project manager at the lake.
The weed, hydrilla, likely arrived from some other infested body of water aboard a boat propeller.
“Now it’s along most of the shoreline, 60 percent or more, from the edges out to 15 or 20 feet,” he said.
Although efforts have been made to control the weed through spot herbicide treatments, the link between hydrilla and deaths of bald eagles and other birds has led some wildlife authorities to call for more drastic control measures.
In certain environments, including Thurmond Lake, hydrilla harbors an unusual algae that is believed to produce a neurotoxin ingested by small birds known as coots that are a favorite food of bald eagles.
The condition, known as avian vacuolar myelinopathy, or AVM, creates brain lesions that have killed at least 60 eagles at Thurmond Lake and many more elsewhere.
Controlling hydrilla could be one step to reducing AVM outbreaks, but any solution could be controversial, and also expensive.
One option under review is the introduction of sterile grass-eating carp. Such a plan, however, might be opposed by anglers who enjoy better fishing around the dense mats of hydrilla.
“These fish are basically goats with gills, and they can grow to 40 pounds or more,” Hyatt said.
The carp have been used successfully in other lakes, including Walter George in west Georgia.
Concerns about using carp include the cost. It would take about $500,000 spread over several years to place the needed number of fish into the lake.
Carp are voracious feeders that would also eat native vegetation, so their impact on other aquatic plant species is uncertain.
Now that a new shoreline assessment has defined the extent of hydrilla infestation, the next step will likely involve a public perception survey managed by University of Georgia researchers to gauge whether there is enough public support to undertake a carp stocking program.
That survey, which will target stakeholders such as anglers and lake-area property owners will be launched next year.
Later, a formal environmental assessment might be required, Hyatt said.
“We could just broaden the chemical treatments we do now, but that only works in certain areas,” he said. “Carp are the only means to completely control it in all the areas.”
The corps will continue to work with stakeholders and resource agencies in Georgia and South Carolina and hopes to devise a plan of action within 18 months.
“That is the goal,” he said. “But there are a lot of variables that could come into play in that 18 months – and from then on out, it would still be funding dependent.”
The shoreline assessment found hydrilla in all major portions of the lake except the western end of Little River and the extreme northern end of the reservoir closer to the Russell Dam tailrace.