Why 600 carp were dumped into the Swift Creek Reservoir

CHESTERFIELD COUNTY, Va. -- Chesterfield County is using one invasive species to fight another in one of the county's sources for drinking water.

The county's Department of Utilities released 600 triploid grass carp into the Swift Creek Reservoir on Tuesday as part of its program to control the hydrilla population in the reservoir. The program has been running since 2010.

The department's director said hydrilla is a non-native, invasive plant originally from Africa and Asia that was first identified in the United States in the 1960s and was confirmed in the reservoir in 2009.

"In a very short period of time, it covered almost half the reservoir and it's a 1,700-acre reservoir," said George Hayes, director of the county's Department of Utilities.

This was concerning to the department as the reservoir provides drinking water to 20-percent of the county's customers.

"It's important for us to protect this reservoir as a long-term drinking water supply," added Hayes.

The county identified the carp as the most cost-effective way to monitor and control the plant as they prefer it as their food source.

"It's very difficult, if not impossible to eradicate it," said Hayes of the plant, which he added often out-competes native species.

Since the hydrilla has taken over the reservoir, county officials have to maintain a healthy balance.

"To have a healthy reservoir, you need a vegetative cover. We would prefer it not be hydrilla, but we prefer hydrilla over having no vegetation for a healthy reservoir," said Hayes. He added that when hydrilla is alive it can be beneficial for the water, but the concern is if there is a mass die-off of the vegetation. "You'd take oxygen from the water column and negatively impact aquatic life and also make treatment more costly."

Since implementing the carp control program in 2010, the county has been moving in the right direction of reaching that balance, which Hayes said is between 20-25% of vegetative coverage in the reservoir.

"In 2017, about 35% of the reservoir had a vegetative cover on the reservoir and in 2018, that's gone down to about 28%," said Hayes.

The county said the program has placed 15,600 carp in the reservoir. Hayes added the total cost since its inception has been approximately $145,000.

Hayes added there is no concern that the carp, also an invasive species, will take over the reservoir or any other body of water it may escape to because the fish are sterilized and cannot reproduce.

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