Hydrilla attack: Lake Anna battles invasive aquatic weed

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Hydrilla is nasty stuff, say Lake Anna residents. Photo by Michael Holahan Hydrilla is nasty stuff, say Lake Anna residents. Photo by Michael Holahan

Lake Anna has shown great hospitality to an unwanted guest for over two decades. Hydrilla, an aquatic weed not to be confused with the mythological nine-headed marsh serpent Hydra, has festered in its waters since 1990.

The bad news (for some) is it’s spreading again. The good news (for all) is it isn’t wrapping itself around boats or wringing swimmers’ legs quite yet. And this time, the Lake Anna Advisory Committee plans to combat it before it does.

The first major infestation took place in the warm side of the lake and infested around 900 acres of the water, according to Harry Ruth, a member of the LAAC’s hydrilla subcommittee.

“It got so bad you couldn’t swim—hydrilla would get tangled up in your arms and legs,” says Ruth, who bought his property on Lake Anna in 1989. The weed grew thickly in the waters by his home, making it nearly impossible to boat.

“If you were lucky enough to get your boat into the water, and if you could get into deep water [that was] greater than 15 feet, you would run into clumps of hydrilla floating around,” he remembers. The clumps came from people who had cut the hydrilla loose—Ruth says he cut through several feet of the hydrilla in front of his property, stacking three or four feet of the weed on the bay.

But fishermen weren’t too upset by the weed and, in fact, they appreciated it as a home for plenty of fish, he says.

In an effort to control the weed without chemicals, authorities introduced approximately 6,200 sterile grass carp, another invasive species, to feed on the hydrilla.

The plan worked and within two years the carp had done their job. But though the invasive weed was mostly gone, Lake Anna’s biodiversity faced a new problem caused by the non-native carp.

According to Virginia Department of Game and Inland Fisheries biologist John Odenkirk, as the carp continued to keep Lake Anna mostly clear of the weed, they also ate and decimated several native species. Over a decade later, Lake Anna’s ecosystem has nearly worked itself out, says Odenkirk, and he’s happy to see the most impressive bass population in 25 years.

Hydrilla is known for its ability to spread like underwater wildfire, and members of the hydrilla subcommittee agree that the remains of it need to be taken care of before the weed causes another scene. This time, though, Odenkirk suggests not “prescribing [grass carp] like a doctor.”

Odenkirk, who is also a member of the subcommittee, wants to use herbicides on the small, affected areas of the lake. But according to Ruth, some of the landowners, including himself, aren’t crazy about the decision.

“Many folks don’t want any additional chemicals put in the lake,” says Ruth, because of the already present chemicals from two power plants and continuous runoff. There are already so many PCBs, or polychlorinated biphenyls, in the water that people are advised to eat only certain quantities of the fish caught in the lake, says Ruth.

For him, grass carp are still the way to go. But in this case, the DGIF wins and herbicides will be used to battle the recent, yet small, hydrilla infestation.

Volunteers will be trained to notice and catalog the hydrilla infestations this summer, and come August or September, spot applications of the herbicide will begin as part of a pilot program.