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Hydrilla horrors: Invasive plant causes bird deaths at lake

Photo by Tori Boone

Photo by Tori Boone

COVINGTON -- There's a problem at Lake Varner. A big one.

The lake has been infiltrated by a fast-growing invasive aquatic plant called hydrilla, and it's wreaking havoc, affecting everything from the water treatment process to the fishing to the bird population.

It's not clear how the hydrilla, which resembles moss when viewed from the surface, got there. But since it was first noticed about five years ago, you might say it's grown at the speed of light. That's not entirely true, sunlight perpetuate hydrilla's growth. Given that Lake Varner is rather pristine, the sunlight can penetrate deep into the lake, and it's creating fertile breeding ground for the plant.

"Hydrilla grows well in Lake Varner. It's very clear water," said Jason Nord, water production manager at Cornish Creek Water Treatment Plant. "It's a protected watershed. The cleaner the water is, the better this stuff grows ... It's worse than dandelions in your backyard. It's unbelievable."

About 70 percent of the 820-acre Lake Varner is now covered in hydrilla. There's no question it's an inconvenience.

Fisherman Frank Newkirk of Jasper County will tell you that.

"It's a nuisance. You just can't fish the banks like you need to. Every time you throw back you come up with a dang line full of it," he said.

Workers at the Cornish Creek Water Treatment Plant can confirm it, too. Lake Varner is the county's drinking water reservoir, and the hydrilla is clogging the intake pipes that pump water from the lake into the treatment facility. It's wrapped tightly around the main intake pump, and though divers have removed it, the stuff grows back in a week or two.

The result is that more water has to be pumped from other intake pipes that are at a deeper level and contain higher levels of minerals like iron and manganese. This water has to undergo more treatment at a higher cost to the county, Nord said.

But there's a much more serious concern: Birds are dying at the lake, including bald eagles.

At least three bald eagles have been found dead at Lake Varner since 2007, according to Dr. Susan Wilde, assistant professor at the University of Georgia's Warnell School of Forestry and Natural Resources, who has been monitoring the situation. Ospreys, Canada geese, and especially coots -- water birds that take up residence at Lake Varner in the fall -- are also being affected.

They're the victims of Avian Vacuolar Myelinopathy, a neurological disease primarily affecting bald eagles and American coots in the Southeastern United States, and there is evidence the source is the hydrilla, or rather, cyanobacteria that grows on top of the leaves of the hydrilla. The cyanobacteria, also known as blue-green algae, contains a neurotoxin that is deadly for birds. Birds affected by AVM after eating it have been found to have brain and spinal cord lesions. They lose muscle coordination and have difficulty flying and swimming.

According to Wilde, these birds will sometimes swim with a list, get stuck upside down in the water, wobble when flying, and even fall from the sky mid-flight.

At Lake Varner, one flew smack into a maintenance building. Nord has seen them fall from the sky and swimming, well, like they're drunk.

"Coots come in the fall and the winter here at Lake Varner and they eat (the hydrilla) and go crazy. They start swimming funny. They swim in circles and they start flying into things," he said. Nord estimates he's seen hundreds of dead coots at the lake during the last few years.

The coots eat the hydrilla, contract AVM and the eagles and other predatory birds eat the coots and it gets passed on. Some water birds have been rescued and kept alive after exhibiting symptoms, but eagles always die within 24 hours after capture, Wilde said.

At Lake Varner, "I've seen Canadian geese so sick I could pick them up and they would not even try to get away," she said.

The toxicity of the cyanobacteria is at its peak when the temperature starts dropping, in late October and November, around the same time the coots arrive at the lake.

"There is no evidence mammals are affected by the disease," Wilde said, but added that more research needs to be done to determine affect on humans.

One study showed that carp that ate hydrilla did develop lesions, but chickens that were fed the carp did not.

"It looked like it didn't move up the food chain through grass carp," Wilde said, adding she doubts that any harm would come to humans who eat fish from the lake, or even hunters who consume the water birds, assuming they are only consuming the flesh and not internal organs.

The toxins do not appear to be in the water, but are closely adhered to the plants, she said, adding that to be affected, a person would likely need to eat the hydrilla itself. Nord said anything that is in the water should be removed in the treatment process.

The county is working with Wilde and with the Georgia Department of Natural Resources to find a solution. While the hydrilla can be managed with chemicals, that is not a viable option because the lake is a drinking water reservoir, and it's also not very effective, Nord said. It can also be managed through mechanical means, but that would be costly and wouldn't totally eradicate the hydrilla, he said.

So, the most ecologically friendly method, and the best chance to thoroughly cleanse the lake, appears to be stocking it with sterile grass carp.

"Carps think hydrilla is like cake and ice cream. They are voracious eaters and they will control this," Nord said.

Grass carp have been used with success to get rid of hydrilla in other locations, including Lake Murray, S.C., Wilde said, but as far as she knows, this will be the first time it has been used on an AVM positive lake in Georgia.

Wilde is assisting the county in pursuing a grant to help fund the stocking of the carp, along with the building of a barrier to keep the fish from flowing downstream into state waters, where they might decimate harmless vegetation. The grant is through the Pulling Together Initiative of the National Fish and Wildlife Foundation to help control invasive species. The Board of Commissioners has yet to approve the grant application. Assuming the board does approve it and the grant is awarded, stocking would begin in the spring with around 4,000 fish.

"It will be an ongoing process for several years to eradicate this stuff," Nord said, noting that stocking of 3,000 to 5,000 carps would need to take place annually for five to seven years.

Though there's no way to know how the hydrilla got into the lake, it could have been carried by a boat from one body of water to another. All boaters are urged to wash their boats and equipment thoroughly before transferring waterways. All residents are asked not to release fish, plants or other animals from one body of water into another.

Anyone who sees sick or dead birds on Lake Varner is asked to call Reservoir Manager Mike Henderson at 770-784-2049 or Wilde at 706-542-3346. Wilde also requests a call from anyone who notices hydrilla growing in other locations.