Grass carp introduced to hydrilla-infested lake

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Duke sends in carp to battle a spreading weed.

Hydrilla could choke water supply from Mountain Island Lake.

By BOB GLENDY, Charlotte Observer

More than 600 acres of an aquatic weed called hydrilla are causing a problem in Mountain Island Lake, which provides drinking water for 1.5 million people in Gaston and Mecklenburg counties.

The plant, native to Africa and parts of Asia, was discovered in Florida in the early 1960s and has spread as far north as the Great Lakes. The concern is that the ropy plant can break loose and block intakes for the three systems drawing water from the lake.

Duke Energy has released thousands of Asian grass carp up to 15 inches long to eat the plants, but the Mountain Island Lake Marine Commission has asked for more.

The sterile fish eat up to five times their body weight, but they can't reproduce, so they won't become too numerous.

Growth of the plant is "a problem we are going to have to manage and it will take a long time to make headway,'' said Mike McLauren, executive director of marine commissions on lakes Wylie, Mountain Island and Norman.

The weed was discovered on Mountain Island Lake in 2000 after Duke made efforts to eradicate brittle naiad weeds. Ken Manuel, weed specialist for Duke Energy, said the brittle naiad causes some taste and odor problems.

"We were checking to determine how effective the chemical treatments were when I discovered the hydrilla,'' he said. "There were about 200 acres of the hydrilla and it has since grown to about 600 acres.''

Manuel said, "no one wanted to put chemicals in a system serving as a water supply for so many people.

Using chemicals would mean closing down Mountain Island, Lake Norman and the water intakes for between 12 and 24 hours.

As for the carp, there was only enough money for 8,000, though the plan was to put in 12,000 back in December. Reports are the carp have made little if any progress in slowing the plant's spread. The plan is to seek another 8,000 carp this year and 8,000 next year.

Manuel said the hydrilla could spread over 1,200 acres of the 3,200-acre lake. That would require 24,000 grass carp and could take as long as 18 months to show signs of improving.

Lawrence Dorsey, Wildlife Commission fisheries biologist, said the consensus of a committee of wildlife officials is to provide additional grass carp.

"Even with the additional carp, it will be 12 to 18 months before we can expect any tangible results,'' he said.

John Huber, water treatment manager for Charlotte-Mecklenburg Utilities, said the carp are part of a long-term balancing act to retain recreation and a water source.

"We don't want to introduce any chemicals that might cause problems with our drinking water supplies,'' he said.

Manuel hydrilla also is in lakes James, Norman and Wateree.

Bob Glendy: The Charlotte Observer, 132 S. Main St., Monroe, NC 28112 ; e-mail basswinr@aol.com.
 

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