MONCKS CORNER -- Hydrilla is an invasive species. So are grass carp. Stocking carp to kill hydrilla is an example of just how provisional the management is over the man-made Marion and Moultrie lakes and prized game fish that keep disappearing.

On Thursday, the state and Santee Cooper unloaded 6,000 grass carp at Angel's Landing and the Hatchery on Lake Moultrie after stocking Lake Marion with as many fish two weeks earlier.

It'a an effort to maintain a population of about 20,000 of the sterile, plant-eating fish to keep hydrilla, a tangling aquatic plant that grows like kudzu, from overrunning the 150,000-acre lake system.

Not everyone approves of the idea. Carp are considered "trash fish" that compete with sought-after catches such as largemouth and striped bass, fish that turned the lakes in their heyday into an estimated $300 million sports tourism destination. Largemouth bass like hydrilla; they gather there for cover and food.

The heyday was back when hydrilla took over, blocking homeowner access to the water and clogging pipes. Working with Santee Cooper, the Moncks Corner-based utility that owns the massive lakes, S.C. Department of Natural Resource biologists turned to the carp to take out hydrilla after pesticides and other controls failed.

"Hydrilla is a non-native and invasive species under federal and state designations, and we are obligated to do everything we can to eliminate it," said Larry McCord, Natural Resources analytical and biological services supervisor. "Grass carp is the most effective solution."

Eliminating the grass carp isn't a question because the fish can't reproduce.

Getting rid of hydrilla is one in a long list of blames why game fish have steadily declined, along with overfishing, stagnation of the lakes and competition from other species eating hatchlings and hatchling food. The carp themselves have occasional mass die-offs.

"I hate it, being a bass fisherman and a duck hunter," said professional bass angler David Goshorn about grass carp stocking. Goshorn of Berkeley County grew up hunting and fishing its lakes and rivers.

The lakes used to be one of the top five bass destinations in the country, he said. Now bass are considered seasonal, something to fish in the spring when they move to shallow water to spawn.

He understands the need to keep water passage open, he said, but not the need to stock carp "until they're eating the bullrushes off the bank."

What Goshorn and other anglers would like to see is hydrilla controlled by stocking fewer carp to allow some plant growth.

DNR, though, has turned to planting eel grass -- streaming underwater runners that make the bottom look like a tall grass meadow. Bass use eel grass like they use hydrilla, and the grass is a native species, McCord said.

Eel grass has helped, Goshorn concedes, and in time might be a bigger factor in restoring and maintaining bass populations.

"But there's really no comparison (to hydrilla). It's a definite asset, but it's not going to solve the problem," Goshorn said.

Reach Bo Petersen at 937-5744 or bpetersen@postandcourier.com.