Fast-spreading weed invades Lake Waccamaw

Fayetteville ObserverAugust 4, 2013 

— Nobody knew what it was at first, just an incredibly fast-spreading aquatic weed near the public boat ramp on Lake Waccamaw.

Rob Emens, an invasive species specialist with the state Division of Water Resources, visited the boat ramp in October and immediately knew it was the dreaded hydrilla.

The weed is so invasive it threatened to choke almost all of the nearly 9,000-acre Lake Waccamaw in as little as five years if left unchecked.

In early June, the state began treating affected areas of the lake – about 600 acres – with a herbicide called fluridone. The state will share the $196,000 cost with the town of Lake Waccamaw and Columbus County.

The lake will need another treatment next month after more surveys and probably a third treatment later this year. Emens estimates the cost will spiral to a total of nearly $500,000 this year and to $4 million within eight years.

He said state officials hope to have hydrilla in check within six years, but there certainly is no guarantee.

Hydrilla was discovered in Lake Gaston, near the Virginia state line, in the 1980s. The plant remains, despite spending as much as $1 million a year in eradication.

Lake Waccamaw, about 12 miles east of Whiteville, is the largest of the Carolina bay lakes and the third-largest of the state’s freshwater lakes. It is home to nearly 50 species of fish and mollusks, many of them considered rare and threatened. One species of endangered fish - the silverside – is found nowhere else in the world.

Left untreated, Emens said, hydrilla would have threatened Lake Waccamaw’s entire ecosystem. Fishing, boating and swimming would have become all but impossible. Property values would have dwindled.

Hydrilla typically spreads from lake to lake by hitchhiking on boat propellers. Left to dry out, it quickly dies, Emens said. But a clump of hydrilla kept damp on a propeller or in a live well can survive for days, even weeks. Once the plant takes root in a lake bed, the nightmare begins.

Hydrilla can reproduce by sprouting plants from stem fragments. But the main nemesis are tubers that settle in the lake bed. Emens said the tubers can lie dormant for years, the main reason eradication is so difficult.

Hydrilla can grow from the lake bed to a height of about 18 feet, making the shallow Lake Waccamaw – its deepest point is only about 11 feet – an ideal host. Once it reaches the surface, hydrilla spreads into a dense, almost impenetrable mat of leaves and stems.

Grass carp, a big Asian fish that feasts on aquatic plants, is one method of controlling the noxious weed. Although considerably cheaper than herbicide treatment, the carp feast on all varieties of a lake’s plants, which can cause an imbalance in the ecosystem if the carp are overstocked.

In the end, fluridone was chosen because it mainly attacks just the hydrilla and does not harm fish or people.

Regardless of the eradication method chosen, the problem is not going away anytime soon.

“Hydrilla is just a huge black cloud over that (lake) right now,” Emens said.

And although improvements in hydrilla management are being made, nothing is on the horizon “that would radically improve the process,” said Rob Richardson, an associate professor and extension specialist with N.C. State University.

Like kudzu, hydrilla was introduced in the United States from Asia for its esthetic value – kudzu for gardens, hydrilla for use in aquariums.

Hydrilla is believed to have been introduced in the wild in Florida in the 1960s. Someone is thought to have dumped out an aquarium containing hydrilla, which escaped into a canal system and then spread into nearby ponds, Emens said. Now, hydrilla can be found in almost every major water basin in Florida.

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