Only in Anne Arundel, where thick residential development exists side by side with a devout love for the Chesapeake Bay, could Keith Underwood become a folk hero.

His name is spoken reverently on the Severn River, where a line of marsh grass now guards the shoreline of the Epping Forest neighborhood. They love his work in Shipley's Choice, where runoff from an elementary school parking lot is filtered through a series of cascading pools.

Underwood designs wetlands, re-creating natural systems in place of pipes and culverts. He is returning tiny, swampy pieces of the county back to the way they were before development.

He is "the Bog Man."

"He has the mind of an engineer, the eye of an artist and the heart of an environmentalist," said Stephen Barry, coordinator of outdoor education for the Anne Arundel public schools.

Underwood, 49, was born in Georgia but has lived in Anne Arundel most of his life. He started out working as a landscaper when he was 18.

More than a decade ago, Underwood says, he became interested in the plants of a disappearing ecosystem, the mid-Atlantic bog. These bogs are differentiated from marshes, swamps and other wetlands by their sandy soil and an array of unusual flora such as the Atlantic white cedar tree, the American cranberry and the carnivorous pitcher plant.

Underwood began to realize that every presentation he watched about bogs finished on the same depressing note.

"Every slide show ended up with, 'The site has been destroyed,' " he recalled.

So he started his own campaign to convince Anne Arundel authorities that the bogs could be brought back.

Fortunately for Underwood, at the same time, local and state governments were also looking at the numerous developments along the water and seeing a problem.

For them, the problem was rainwater. Before the homes and streets were built, the county's forests had absorbed the water and allowed it to filter through soil and plant roots.

But after development, the water blasted off roofs and through streets and storm drains. It carried large amounts of dirt, which clouded the waters of the rivers and the Chesapeake Bay. The unfiltered storm water also carried nitrogen and phosphorus, pollutants that are blamed for large algae blooms and oxygen-poor "bad water" in the bay.

Underwood began to make the case that bogs could filter the water better. At first, officials were not inclined to listen.

"We saw him as kind of maybe an obstructionist," said Dennis McMonigle of the county public works department.

But gradually, Underwood was able to demonstrate his techniques on small projects. One of the earliest, in the early 1990s, was a cranberry bog he created in the Sherwood Forest neighborhood that filtered some of the waste from leaky septic tanks.

Kevin Smith, of the Maryland Department of Natural Resources, said he thought the first hard rain would blast the entire bog away. "It was a head-scratcher," he said.

But that didn't happen: The bog survived and filtered away some of the pollution.

"The whole time, everybody that I knew was telling me to get back to work and stop playing in the bogs," Underwood said. "We're all happy that I didn't listen to them."

In 1997, Underwood got his biggest break. He was asked to renovate the muddy valley of a stream called Howard's Branch, between Sherwood Forest and the Downs in the Severn neighborhood outside Annapolis.

The valley had once been a wetland, but in the 1930s the creek was dammed to form a drinking water reservoir.

The dam broke in the early 1980s, and when the water ran out it left behind a thick field of sediment that Underwood compared to chocolate pudding. The creek began carrying out enough dirt to cloud nearby Brewer Creek, a Severn tributary.

The valley was a kind of wetland, Underwood said, but not the kind the area needed.

Fixing it took 58 days of construction and $350,000, provided by the Maryland Department of the Environment and the Anne Arundel County Department of Public Works.

First, Underwood's team laid a special kind of cloth over the shifty sediment. On top of that they spread a huge amount of white sand, of a local type crucial to the bog ecosystem.

The stream was then re-channeled to form several pools, divided by piles of cobblestones. Storm water could pool and slow down as it flowed through, instead of blasting away dirt down toward the Severn River.

Then they planted 1,000 Atlantic white cedar trees, grown from the few remaining west of the Chesapeake Bay, on the site.

Then Underwood and his team waited for nature to do its work.

What formed was a system in which water first pools, then filters underground through the sand. The wet sand supports a variety of plants, including a growing carpet of moss and algae.

"This is really exciting here, believe it or not," Underwood said, walking through the area one recent day. He was pointing at algae growth that -- were it found in an aquarium or an ice machine -- might be called slime.

"That's the primeval bog right there," Underwood said.

Eventually, he said, the dead plant matter will form peat, which will also trap sediment and pollutants.

For now, Underwood said, the Howard's Branch system attracts seven species of frogs and the spotted salamander, plus sunfish, deer and other animals.

Barry, of the county school system, said visiting it is "like going to Shangri-La."

To once-skeptical authorities, the Howard's Branch project helped seal Underwood's reputation. Though many people across the country work to restore wetlands, experts said few of them restore this type of bog with such faithful attention to local detail.

"Over time, we kind of realized, 'Hey, Keith is right about this stuff,' " McMonigle said.

Underwood has worked on projects across the county, helping him to earn his nickname, the Bog Man. They include a bog in the Shipley's Choice neighborhood, and a system of terraced pools to filter storm water at nearby Shipley's Choice Elementary School.

There were also projects called "living shorelines," such as the one in Epping Forest. There, Underwood put out a series of rocks and planted grasses behind them. He believes that kind of man-made wetland will help stop erosion and filter water, an improvement over bulkheads or riprap.

Right now, he is working on a half-million-dollar project at the North Grays Bog, off the Magothy River near the town of Lake Shore. There, again with funding from the county, he is trying to restore a bog that was ruined when dredged-up mud was dumped there decades ago.

On one recent visit, the project looked like any construction site: There were backhoes and dump trucks, and big fields of mud.

But soon, Underwood hopes there will be a meandering series of pools, lined with magnolia trees, cranberries and sundew plants.

"You're going to look at this evergreen savannah out there," he said.

Living in the restored stream at Howard's Branch are macroinvertebrates, left, and a carnivorous purple pitcher plant, right. Algae, left, stabilizes the sand that was poured at Howard's Branch and allows plants, such as the goldenrod at right, to establish. Keith Underwood, from far left, demonstrates the health of the bog he recreated at Howard's Branch by pointing out new, wild growth. "That's the primeval bog right there," he said as he surveyed. Below, his license plate.