Study finds no hydrilla in Mountain Island Lake

by Tori Hamby

A recent study of Mountain Island Lake by Duke Energy found no hydrilla, a lake-clogging weed known to disrupt aquatic ecosystems and interfere with efforts to treat the area’s drinking water.

To combat hydrilla, Duke Energy has partnered with the North Carolina Department of Environment and Natural Resources, Charlotte-Mecklenburg Utilities Department and the City of Gastonia for more than 15 years. Each year, officials stock Mountain Island Lake with triploid Asian grass carp, a species of fish that feeds voraciously on hydrilla sprouts.

“The Asian grass carp is an obligatory herbivore, which basically means it’s a vegan. It eats nothing but salad,” said Ken Manuel, a senior scientist at Duke Energy.

While there may not be any hydrilla weeds growing in Mountain Island Lake right now, Manuel said hydrilla tubers, or reproductive structures, can lie dormant in the lake’s soil for up to 10 years. Waterfowl, such as ducks and geese that eat the plants, can bring the dormant tubers into a lake environment via their waste.

This sneaky method of reproduction forces officials with the program to annually restock the lake with about 500 carp. Each fish, bought from fish breeders for about $3.50 to $5 apiece, is bred to be sterile and has a life expectancy of about 10 years. The state Department of Environmental and Natural Resources pays for half of the cost of the fish, while the utility, City of Gastonia and Duke Energy split the cost of the remaining half.

While some cities and counties use herbicides to kill off invasive species, Manuel said, that method is not an option for Mountain Island Lake because it supplies drinking water to more than an estimated 1.5 million people in Mecklenburg and Gaston counties. The carp, which are continuously on the lookout for food, also find and consume tiny hydrilla sprouts before they develop into weeds, which get tangled up in boat propellers, interfere with intake at water treatment and power plants and grow uninhibited due to a lack of any natural controls.

“When (the carp) see a sprout coming from those tubers, they nip that off,” Manuel said.

If the program’s cooperators allowed hydrilla to grow uninhabited, the weed would cover about 1,000 acres of the lake, he added.

“I would say that hydrilla is probably the worst invasive plant in North America,” he said. “It does millions of dollars of damage across the southeastern United States.”

Rusty Campbell, with the Charlotte-Mecklenburg Utilities Department, also said that the weeds can cause several issues with the city’s water supply.

“The aquatic weeds in general can clog and slow down our intake, and some can contribute to taste and odor problems with the water supply,” he said.

According to Manuel, the uncontrolled growth of invasive plants and fish can become a problem anytime a new species is introduced into an ecosystem or environment. In the case of hydrilla, most likely native to the tropical regions of Africa where sunlight does not penetrate water as easily, unfiltered sunlight reaches the lake’s bottom causing the weed to flourish. Hydrilla and hydrilla tubers can be found in most the area’s lakes, including Lake Norman, Lake Wylie and Lake James.

To help combat the uninhibited growth of hydrilla or other invasive species, lake users should not dump any living thing into the lake, including plants from rain gardens or unwanted fish or plants from aquariums, Manuel said.

“The essence is that no one should introduce living materials into the lake, which means aquariums and excess materials from a water garden that someone might have growing behind their house,” Manuel said. “Inevitably, we find goldfish that are 20 pounds swimming around docks and all kinds of exotic species growing in the lake.”

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