2015-05-06 / News

Carp corps sent in to take down reservoir’s hydrilla

By Jim McConnell

Last week, 1,000 sterile carp were pumped into Swift Creek Reservoir to manage fastgrowing hydrilla, a persistent problem. 
Courtesy of the Chesterfield County Public Affairs Department Last week, 1,000 sterile carp were pumped into Swift Creek Reservoir to manage fastgrowing hydrilla, a persistent problem. Courtesy of the Chesterfield County Public Affairs Department Local officials have summoned reinforcements in their battle to prevent an aggressive aquatic plant from overwhelming one of Chesterfield’s drinking water sources.

Workers from the county’s utilities department introduced a second wave of sterile carp into the Swift Creek Reservoir last week in the hope that the 1,000 grass-eating fish will help further control the growth of hydrilla in the 1,700-acre lake.

“We knew at some point we’d have to restock the reservoir,” said George Hayes, the county’s director of utilities.

Officials aren’t sure exactly when or how hydrilla – a fast-growing plant native to Africa, Australia and parts of Asia – originally got into the reservoir. But they’ve been dealing with it since 2009, when extensive shoreline growth on the Brandermill side of the reservoir made it difficult for many of the community’s waterfront homeowners to launch their boats.

Hydrilla is basically impossible to eradicate. Recognizing the plant’s potentially adverse impacts on the local drinking water supply and property values, the county paid a Connecticut-based consultant $23,000 to study its presence in the reservoir and develop a plan to manage it.

The consultant, Kenneth Wagner, an environmental biologist, came up with three options to control the hydrilla: chemical, mechanical or biological. The latter was identified as the most cost-effective and environmentally friendly option.

In April 2010, the county paid another $40,000 to stock the reservoir with 10,500 carp.

At that point, hydrilla covered about 54 percent of the reservoir. Within about 18 months, the carp had significantly reduced the problem.

“The carp worked really well,” said Charlie Davis, an owner of lakefront property and president of the Brandermill Community Association board of directors. “When they’re eating, it’s a feeding frenzy. It’s interesting to watch.”

Hydrilla experienced a resurgence last summer. When the utilities department used a series of underwater cameras to study the plant’s growth last October, they estimated that it covered approximately 425 acres of the reservoir.

The bitterly cold winter took care of that problem. There’s currently no hydrilla growing in the reservoir, Hayes said, but “we know it’s there and we know it’s going to come back.”

Carp grow quickly because they’re able to eat their weight in hydrilla on a daily basis, but their activity level decreases as they mature. As a result, they’re less able to keep up with the plant, which can grow an inch a day under optimal conditions.

While carp can live between 10 and 15 years, they have a mortality rate of up to 20 percent – and that doesn’t take into account the fish that have been plucked out of the shallow water by predatory birds.

Because the carp are sterile and unable to reproduce, county officials knew that to avoid letting hydrilla regain a foothold in the reservoir, they’d periodically have to purchase additional fish.

Based on mortality rates and estimates from the Virginia Department of Game and Inland Fisheries, which uses a device to temporarily shock the fish and bring them to the surface of the water to be counted, Hayes estimated that about 3,500 of the carp originally introduced into the reservoir are still alive.

“There’s no easy way to say for sure how many fish are left,” he said. “It’s not an exact science.”

The 1,000 carp introduced into the reservoir last week cost the county $7,740, including transportation from a farm in Arkansas.

“I believe we took the right approach, hitting the problem hard initially,” Hayes added. “Managing it is a different story. We don’t have to be as aggressive, and we don’t need as many fish since we’ve gained control.”

Some county residents have balked at the allocation of taxpayer funds to maintain a lake that isn’t accessible for recreational uses by the general population.

In a September 2014 letter to the Observer, Michael Glowinski suggested that the inconvenience hydrilla caused for boaters in Woodlake and Brandermill was the real reason why the county originally deployed the carp.

“The land under the water is private property. The residents are very adamant about that, but they have no problem with the taxpayers cutting their grass on their private property so they can use their private boats on their private lake,” Glowinski wrote. “Is the county going to send them a bill? Not a chance!”

Deputy County Administrator Bill Dupler has noted that the county government’s only interest in the reservoir is as a water source. The reservoir supplies about 20 percent of the county’s drinking water.

“It’s been in operation for nearly 50 years,” Dupler said, “and it has a long life ahead.”

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