It would not be accurate to call Floating Island International, the business led by Bruce and Anne Kania, a mom-and-pop operation -- for one thing, although they are married, Bruce and Anne don't have children -- but that description gives you a sense of the scale of their startup. With fewer than a dozen employees, the Kanias are tucked away in the small town of Shepherd, Montana (population: 208) and the firm's annual revenues are less than $1 million.

But Floating Island International already lives up to its name: Its man-made islands can be found in New Zealand, China, South Africa and Canada as well as in the U.S. Its customers include U.S. Army Corps of Engineers, American Electric Power and Disney World, which suggests that they may be onto something. And the Kanias' ambitions seem to know no bounds.

"I'm pretty sure we are going to be one of the most successful businesses of all time," says Bruce.

Bruce, who is 57, is an inventor and entrepreneur who worked in prosthetics, textiles and sporting goods (he invented a broadhead arrow). Then, about a decade ago, he came up with the idea of turning plastic trash into man-made floating islands that can clean polluted water, spur the growth of fish, provide species habitat and sequester carbon.

Not to mention create beachfront property.

"We're learning how to grow real estate," he says.

I met Bruce and Anne recently at the Society of Environmental Journalists conference in Missoula, MT. Their company is just five years old, they told me; it was inspired by the floating peat bogs of northern Wisconsin, where Bruce grew up and worked as a fishing guide. He graduated from the University of Wisconsin with a degree in social studies, and much later bought a farm on the Yellowstone River in Montana.

His business got started with a smelly dog named Rufus. The pooch jumped into an irrigation pond on the farm and emerged with a stinky, reddish tinge. The water was overloaded with nitrogen and phosphorous, runoff from nearby farms and ranches -- the same kind of runoff that pollutes waterways everywhere, from the Mississippi River to Chesapeake Bay to the New Jersey-sized dead zone in the Gulf of Mexico.

What might be done to clean up the pond, Bruce wondered. He had by then heard of biomimicry, a term coined by biologist Janine Benyus, another Montanan, to describe a discipline that draws upon nature's designs and processes to solve human problems. (See Buildings inspired by nature at Fortune.com) Says Bruce:

It was so extreme and graphic that it drove me to ask the question: How does nature handle this? Nature handles it with wetlands. This concept of using nature as a model seems a lot more elegant that the bombs and bullets approach of turning to a chemical solution or mechanical device. It's a vision of trying to live more in harmony. So how can you develop more wetlands?

What followed were dozens, if not hundreds of prototypes. "It's not that a light flashes and here's your invention," says Bruce. "It evolves." His man-made islands had to be porous enough so that lots of water could flow through for cleaning, and yet solid enough so that plants could grow on them, like this peat bog:

Eventually, Bruce and Anne decided to build their islands out of post-consumer PET, like this:

They are then seeded with native plants suitable for wetlands:

After a growing season or two, they look like this installation, one of a series of islands found in a stormwater pond in suburban Chicago:

About 400,000 islands have been built using Floating Island's intellectual property. Most are small -- they can be put in a backyard pond -- but this year the company has commissioned four islands that are more than 20,000 sq. ft. Two of the biggest were bought by the Army Corps of Engineers and located in Dutchy Lake, Oregon, and Sheepy Lake, California, to act as nesting habitat for Caspian terns. The goal was to get the terns to locate away from the Columbia River, where they were preying on migrating baby salmon. (The designers placed 250 tern decoys on the island to lure the birds.) Early results are promising.

The Kanias and their employes make some of the islands in Shepherd, frequently for research purposes. (The Kanias have grown tomato, raspberry, asparagus, watercress and wild ginger on their islands.) Most are built by eight firms — six in the U.S., and one each in China and New Zealand — that have licensed their technology. They cost about $30 per square foot. You can read a lot more about the islands, and how they work here.

Bruce has a big idea, literally, for a floating island he calls Leviathan that, when equipped with mechanical aeration, could circulate and clean up to 1 million gallons of water per minute. He had hoped to test one out to clean up the BP oil spill, and enlisted the help of Sen. Jon Tester of Montana, but so far, he hasn't found a buyer. Most of his customers so far are municipalities that want to clean up their local water supplies.

Eventually, he's hoping to expand the supply of oceanfront real estate, he tells me. There's no limit to how many islands can be lashed together, and larger ones can be anchored, he explains.

"Bruce is being a little coy here," Anne says, "but he's talking about growing his own country."

The inventor smiles.

"Wouldn't that be fun?" he says.

GreenBiz.com Senior Writer Marc Gunther is a longtime journalist and speaker whose focus is business and sustainability. Marc maintains a blog at MarcGunther.com. You can follow him on Twitter @marcGunther.