My friend Elizabeth Johnson is a boat captain on Tybee Island. For a living she takes anglers 50 to 75 miles off the coast and tells them how to bait up and where to cast and how to reel in. She’s the kind of person who goes at life like Earl Scruggs goes at banjo, which is full tilt boogie.

Thirty percent of the salt marsh in the U.S. lies off the Georgia coast, and it’s a beautiful wilderness out there, an immense and salty meadow of spartina cut by water trails. The marsh is a labyrinth of tidal creeks and big lazy river-mouths, a territory made more confusing by the inconstancy of draining and filling.

"What keeps you from getting lost?" I ask Elizabeth. "Is it mapped in your head?"

"I don’t always know where I am," she says. "Sometimes I take a wrong turn."

But after 20 years of boating she knows more than she lets on, and as we zoom past this island and that, Elizabeth points out where there are oysters, where the camping is good, where the cedars grow thick. We never use the nautical charts.

Going home the tide’s receding, exposing black mudbanks that flower with egrets, willets, great blue herons, oyster catchers, and sandpipers. At South Cut Elizabeth spots something in the water. It has ears, and big brown eyes. It’s a deer, swimming! The water’s deep and cold and wide, maybe 300 feet across, and we stall the boat and watch the doe plow through the waves. It looks doubtful she’ll be able to climb the 6-foot cutbank. But when she breaks free of the water the deer leaps the embankment in a spray of flying water. She disappears into the hammock.

"Anything is possible," that leap says.

Horsepen Creek is half empty by the time we turn up it. Elizabeth slows, concentrating on the channel to keep the boat from grounding. Then we notice the dolphins. A pair of them break water just ahead, arching and rolling in that fluid, silvery way they have.

"Oh," Elizabeth exclaims. "We can follow the dolphins in."

I look at her. "They follow the channel?"

She smiles and nods yes. We putter behind their sleek forms underwater. When the dolphins exhale, they send up sudden mists.

Once the dolphins pause to press a little school of fish against the shore and there is a general thrashing-about as they feed. Then they continue up-creek.

When we dock it is almost dark and a loon is calling.