CLAYTOR LAKE — Six thousand sterile grass carp were released in three areas of Claytor Lake early Thursday morning, drawing a crowd of onlookers, residents and wildlife specialists.

The fish eat hydrilla, a plant that covers an estimated 400 acres of the more than 4,000-acre lake. The monster vegetation has caused concern among homeowners, business owners and officials in Pulaski County.

John Copeland, fisheries biologist with the Virginia Department of Game and Inland Fisheries, said officials hope this will help them start to get the hydrilla problem under control.

“At Claytor, it’s going to become a boating and navigation issue,” he said.

The lake water was just 56 degrees Thursday morning, an important consideration for transferring the fish from the hatchery. When the lake gets warmer, the fish can get stressed.

The plant-devouring carp average about 13 inches long. Thirty-four of the largest ones were tagged with radio transmitters for research purposes. The fish won’t erase the hydrilla completely but could help bring it down to a “dull roar,” said Lloyd Hipkins, an extension weed specialist with Cooperative Extension at Virginia Tech.

The county budgeted $12,540 for the fish to be brought from Arkansas and distributed, with oversight by DGIF.

“A biological control like a grass carp lasts a long time and is cheaper than spraying,” Copeland said.

Although many people will be happy to see the plant go, there are others who are worried about losing it — mainly anglers who say that cutting back the hydrilla will hurt fishing habitats and that chemical sprays will kill fish.

Along with the carp, plans call for chemicals, specifically Komeen, to be sprayed on hydrilla in the lake this summer, paid for by a $50,000 grant from Appalachian Power Co.

A former professional fisherman and a businessman on the lake, Rock House Marina owner Mike Burchett can see both sides of the hydrilla debate.

Burchett is a member of the committee of Pulaski County officials, the citizens group Friends of Claytor Lake, business owners and wildlife experts that has been planning the most substantial collaborative effort to date to fight what they call the “hydrilla gorilla.”

For fishermen, it’s a bonus because, if it’s not too thick, hydrilla provides cover for fish, Burchett said. But left unattended, the plant can decrease oxygen in the lake and hurt native habitats.

The plant is often introduced into lakes by boaters who have picked it up in another lake, which is why education is important, Burchett said. Its tubers and seeds can also be transported by animals.

Hydrilla makes a good fish habitat for a few years but will cause more harm than good if left untreated, said Mike McLeod of the Virginia Department of Environmental Quality.

Chemicals have been sprayed by private contractors hired by residents to treat hydrilla on Claytor Lake for three or four years, and “there are no records of direct cause and fish kills,” McLeod said.

Plans call for the use of Komeen, a contact herbicide. It contains copper, but the copper in the herbicide is biologically inactive, McLeod said.

It also kills the plant only where it makes contact, unlike a systemic herbicide, which goes throughout the plant.

“There’s really no reason to believe it’s going to hurt any fish,” Hipkins said.

For now, researchers from DGIF and the Virginia Tech department of fish and wildlife conservation will monitor the grass carp movement and eating habits in the lake.

The fish are made sterile in the hatchery — DGIF requires all non-native fish brought into Virginia waterways to be sterile to avoid invasive species being introduced, Copeland said.

In August and September, the plant’s peak growth times, specialists will study the plant growth to decide how many fish will be needed next year.

“They can’t put enough fish in there to take care of the problem the way it is, so what they’re trying to do is integrated management and kill a good portion of it,” Hipkins said. “If they can use the fish to maintain a very low level, then ultimately the business about treating with chemicals could go down year after year.”By Amy Matzke-Fawcett