CLARKS HILL, S.C. — No one is quite sure when the first tiny sprig of hydrilla found its way into Thurmond Lake.
By the time of its 1995 discovery near Cherokee boat ramp, the invasive, exotic weed – once a staple of the aquarium trade – had already infested several acres. Today, it occupies 640 miles of the lake’s shoreline, with known patches totaling 4,959 acres.
This fall, about 8,000 anglers, property owners and other stakeholders will be surveyed about the prospect of introducing a new fish to the reservoir – sterile, grass-eating carp – as a means of controlling hydrilla.
“We try to spot treat with chemicals, but usually just around a few boat ramps and navigation channels,” said Army Corps of Engineers biologist Ken Boyd. “It is not an overall or complete program.”
Thurmond is one of the major sites in the Southeast where hydrilla harbors an unusual algae linked to a fatal neurotoxin that kills bald eagles.
Scientists believe infected hydrilla is eaten by small birds known as coots that are a favorite food of eagles. The resulting condition, known as avian vacuolar myelinopathy, creates brain lesions that have killed at least 60 eagles at Thurmond Lake alone.
The prospect of using grass carp to eat the hydrilla, and possibly reduce eagle mortality, is the main focus of the survey, said Susan Wilde, an assistant professor at University of Georgia’s Warnell School of Forestry who is part of a research team studying AVM.
“We’d like to get a wide range of perceptions,” she said.
The surveys will be sent to hunters, fishermen, campers, boat owners and property owners, followed up by 6,000 reminder cards.
“The Corps of Engineers feels like this will give them an idea of what the differing opinions are,” she said. “And we also want the public to be informed on all the options and ideas.”
Use of grass carp in the 70,000-acre lake would require coordination, and possibly funding, from multiple sources, including Georgia and South Carolina, which share the lake and its resources.
Possible concerns about using carp include the cost – estimated at $500,000 spread over several years. Carp are also voracious feeders that might affect native vegetation.
“We know that hydrilla and its presence in the lake has both supporters and detractors,” said fisheries chief John Biagi of Georgia’s Wildlife Resources Division. “To come up with a decision on how to handle it, a public stakeholder process should be engaged to be sure the corps is making the right decisions on control methods.”
Hydrilla clogs channels and creates navigation problems, but it also provides benefits, such as cover for sportfish.
“There are a lot of things being juggled, and we have to find the best solutions,” Biagi said.
Sterile grass carp have been used for decades in private ponds, golf course lakes and many other environments, but introducing them to one of the largest lakes in the eastern U.S. will require a lot of coordination – and a certain level of caution.
Georgia authorities require a state permit for introducing the carp into larger bodies of water, and typically require a barrier of some sort to make sure the fish do not move into state rivers or streams.
The most recent Georgia site permitted for a large scale stocking of grass carp is Newton County’s Lake Varner, an 800-acre reservoir near Covington that has become choked with hydrilla – and where AVM has also been detected.
“We’ve ordered 4,000 or so 10- to 12-inch fish, hopefully to be stocked in the next month,” said Jason Nord, the water production manager at the lake’s Cornish Creek Water Treatment Plant. “We’ve had hydrilla about 10 years, but it has really worsened in the last five years.”
Newton County explored several means of weed control, including herbicides and mechanical removal, but concluded the carp would be the most effective. As a condition of receiving a permit, a $57,000 fish barrier was built to prevent the lake’s carp from escaping into nearby streams.
Although the corps is exempt from state permitting authority, the federal agency would involve both Georgia and South Carolina in a series of environmental assessments – and possibly public meetings – that would precede any final decision on stocking carp at Thurmond Lake.