FOLKSTON, Ga. (AP) — Nature isn't kind to overnight camping platforms at the Okefenokee National Wildlife Refuge.

If periodic wildfires don't destroy the wooden shelters, humidity, high water and wear and tear from campers takes an exacting toll in 15 to 20 years.

Upkeep is important because of high demand to camp on the 20-foot-by-28-foot structures standing about 3 feet above the water in remote areas in the swamp. Gracie Gooch, a refuge ranger, said as many as 7,000 visitors camp each year on the swamp's seven overnight platforms.

Because the refuge doesn't have enough staff to maintain the structures, volunteers often do the painstaking, back-breaking work.

"If it wasn't for volunteers, we wouldn't be able to keep up with the maintenance," Gooch said.

Recently, a group of volunteers loaded flat-bottom johnboats with heavy wooden beams and planks, a generator, tools and other equipment. They launched the boats at the Kingfisher Landing entrance north of Folkston and headed 8 miles west over the glassy surface of the swamp's black water trails.

At the Bluff Lake platform, they found its aging wood sagging under the weight of a prefabricated outhouse.

The volunteers learned techniques to maintain the platforms are often as primitive as the camping conditions.

They drove 16-foot pilings into the murky water using nothing but muscle power and body weight. Then, they hammered planks onto the pilings and cut a carefully measured hole where the tank of a new outhouse was sunk.

They couldn't sink the tank deep enough at first because of obstructions under the new section of platform. They used rakes and their hands to remove floating chunks of peat and grass so they could install the tank properly.

"This is a major project," said Bill Chilson, a volunteer from Pennsylvania who has worked at the swamp since September. "It's a little intimidating the first time out, but you get used to it."

The swamp teems with wildlife, including black bears, venomous snakes, biting insects, thousands of alligators. Others such as otters, wading birds, eagles, deer, frogs and foxes, are less threatening.

Sam Williams of Folkston is another volunteer who helped with renovations.

"I think it's the best-kept secret around," he said of camping overnight on one of the platforms.

Volunteers are required to take safety classes before operating chain saws, drills and pumps and other power tools at work sites.

Gooch said the old outhouse and support structures will be removed sometime in March after a cabana to cover the new outhouse is installed.

"We can probably do it in a couple of days," she said. "We're hoping we can do it by hand."

Charlton County native Jackie Carter, a volunteer who supervised the work, said the goal is to quickly perform maintenance without interfering with canoeists and campers. Campers aren't allowed on the platforms for safety concerns during maintenance.

Volunteers worked as long as 12 hours a day to finish the project quickly, he said.

Demand for the campsites peaks in early March through the end of May because the temperatures are moderate, the humidly is low and the bugs aren't swarming. The refuge attracts about 400,000 visitors a year.

"We try to watch out for the public," Carter said. "We want them to have the best experience when they come to the swamp."