One of the world's largest farm tractors is plowing under soil laced with pesticides along Lake Apopka, where a decade ago an attempt to turn former farms into wetlands brought disaster.

State water managers think an enormous plow will render nearly 5 square miles of contaminated cropland safe for flooding, an essential step to reviving one of the sickest large lakes in Florida.

The first try at converting the farmland into marsh failed in 1998. It killed more than 1,000 eagles, storks, pelicans and other birds that ate fish which had become toxic with pesticides seeping out of the soil.

The giant tractor will put the deadly dirt far out of reach, state officials say, while adding $7 million to restoration costs already exceeding $115 million.

"We are turning the soil 180 degrees, bringing up bottom soil and putting it on top of the topsoil," said Johnny Allen of Roscoe, Texas, who was hired to do the work.

At 35 tons, 40 feet long, 12 feet tall and powered by a 600-horsepower diesel engine, the tractor plow that Allen brought to Lake Apopka is as much earthquake as earth tiller. It rolls not on tires but on rubber tracks 30 inches wide. That's so it floats over muck that a person walking across would sink through.

Combining heavyweight power with light footing gives it the ability to slog into sloppy soil and still pull four plow disks that are 52 inches across. Despite their extraordinary size, the circular blades slice Apopka fields as easily as if it were chocolate cake.

Scientists figure the top foot of soil harbors most of the dangerous residues from DDT and other now-banned pesticides. With that in mind, the disks were designed to gouge up clean dirt from 3 feet deep, shove it to the surface and dump toxic topsoil into the void.

Every dozen feet, the disks plow enough ground to fill a large dump truck.

"It'll blow your mind when you figure out how much dirt we turn," said Allen, who put the amount at hundreds of tons a minute.

For the past quarter-century, Allen has coupled some of the world's largest tractors with some of the largest plows, which he hand-builds, to take on the stubborn clay of the Texas Panhandle region. The machine he brought to Lake Apopka is his most massive yet.

Still, it's tedious plowing, hindered by outcrops of limestone, equipment breakdowns and getting stuck. When that happens, the extended Allen family rolls in with an armada of slightly lesser tractors to yank the stranded beast out of its quagmire.

Allen hopes to plow 20 acres a day. It's an expensive process but still much cheaper than digging up and hauling away the thousands of acres of contaminated dirt.

Allen's crew also must grade, smooth and compact the ground, requiring, in all, a dozen passes by tractors. Such a pace, coupled with weather delays and trips to Texas, could keep them turning the dirt of Lake Apopka's shore for nearly two years.

When it comes to restoration of Lake Apopka, the state's fourth-largest lake, time passes at its own pace.

Since the 1980s, the state has bought 20,000 acres of farmland along the 50-square-mile lake in Lake and Orange counties. The goal was to stop and undo damage from decades of farms pumping their dirty runoff into Lake Apopka.

The practice killed the lake as a fishing and natural paradise and fed uncontrollable algae that turned Apopka a vivid green.

By late 1998, the last of the farms were bought, flooded and thought to be on their way to becoming marsh that would help cleanse the lake.

Yet that turned horrific when authorities began to discover birds either dead or in the final stages of acute pesticide poisoning. For years afterward, the threat of federal prosecution and lack of scientific understanding of the bird kill all but shut down restoration.

Now, at least work is under way, relieved officials say.

"It's really pretty exciting because after all these years we're getting close to flooding again," said Dave Walker, a restoration project manager.

For Allen, the Lake Apopka job isn't so unusual. His tractors also have plowed soil oozing with oil and mining sites laced with arsenic. Yet, he's envious of Apopka's rich dirt.

"You could grow anything in it," said Allen, who would like to plant a crop or two but recognizes Florida's investment in a new future for the former farmland.

"When we're done here, it won't have any pesticide, herbicide or any kind of contamination in it," he said.

Kevin Spear can be reached at kspear@orlandosentinel.com or 407-420-5062.