Pupils from Chesapeake Academy in Arnold, including Riley Dulaney, 11, right, and Kendall Gay, 10, center, are given an education about the reconstruction of Poplar Island before releasing their turtles into the wild. (Sarah L. Voisin/THE WASHINGTON POST)

Stepping off the gravel road encircling Poplar Island, I walked gingerly down a small hill, salt meadow hay crunching beneath my feet.

“Keep going,” urged Laura Baldwin, our guide. “Slowly.”

I took a few more steps, and suddenly, just feet in front of us, a mallard flew up from a hidden spot in the field. Baldwin walked to where the duck had been sitting, lifted a flap of grasses and revealed a nest of nine perfect eggs. I inched closer, delighted. This wasn’t what I’d been expecting when I signed up for a tour of the island, but for our first stop, it was a good start.

Details, Maryland’s rebuilt islands

For years, when I visited Tilghman Island on the Eastern Shore of the Chesapeake Bay, I’d heard about Poplar, and I knew that the critically eroded island was being rebuilt as a wildlife habitat. I’d seen it from afar by boat and had conjured up an image that wasn’t too far removed from Jurassic Park — a land thick with prehistoric plants and large, bizarre-looking animals.

But as the tour boat approached the island one morning in May, I saw minimal vegetation, long-necked excavators and dump trucks filled with earth. It was only then that I realized I knew nothing about this place, except that I’d have to relinquish my dinosaur fantasy.

Poplar Island is a work in progress, but it’s still one of the coolest free tours I’ve stumbled upon. The island, 12 miles south of the Bay Bridge, is one of several sites that Maryland is rebuilding, using material dredged from the bay’s shipping channels. To keep the shipping industry competitive, the state has to deepen the bay by an average of 21 feet to accommodate large cargo ships, which need 50 feet.

It’s an ongoing challenge to find space for the roughly 5.2 million cubic yards of sediment that Maryland dredges each year (imagine FedEx Field filled to the top 21 / 2 times), but the state has come up with a clever solution: Restoration sites offer a space for the material while also providing desperately needed wintering and nesting spots for migratory and local species.

Currently, three sites offer public tours, and a fourth will open later this summer. It’s fascinating to watch the projects midstream; the engineering behind building islands and wetlands is remarkable.

On Poplar, after ogling the mallard eggs, we hopped aboard our tour van and continued driving around the boomerang-shaped island. Baldwin pointed out a thick grassy area that was part of the original Poplar.

We learned that the island once consisted of 1,100 acres and was home to about 100 residents — in the mid-1800s, there was a church, a general store and a sawmill, which ate up all the trees and helped contribute to erosion. In 1929, the national Democratic Party bought Poplar and neighboring Jefferson Island, where it built an exclusive men’s-only hunting club. Presidents Franklin D. Roosevelt and Harry S. Truman were among the visitors.

By the 1990s, Poplar had eroded to barely five acres. So a team of federal and state agencies, headed by the Army Corps of Engineers, the Maryland Environmental Service and the Maryland Port Administration, decided to restore it and started construction in 1998. When it’s completed, in 2039, it will include 1,715 acres of tidal wetland, upland and open-water habitat.

Building islands is an exhaustive process. You build the outside first, the way you would a jigsaw puzzle. A dike forms the perimeter, and barges deliver the dredged material to the interior. The sediment gets mixed with water to create a slurry — it looks like Nesquik — that’s deposited using mechanical or hydraulic unloading. Then the excess water is drained out, which can take years.

The island looks at times like a big science experiment. “This project is one of the first of its kind,” Baldwin said, noting that it has attracted international visitors. “We have what we call a trial-and-error plan.” For instance, more than 50 species of trees have been planted, and those that grow well in the dredge material will be scattered throughout an adjacent area that will become a forest.

As we drove, we saw a bald eagle flying overhead, an osprey nesting, a muskrat and a snake swimming, dozens of toads the size of Brussels sprouts, a duck followed by a half-dozen ducklings, cormorants occupying a small island, and a red-legged black-necked stilt walking in the sand. The sky was busy with the chattering of terns, willets and red-winged blackbirds.

Each fall, after diamondback terrapins hatch, some of them are loaned to Maryland schools, where kids raise them until the spring. Growing in captivity gives them a head start on wild living. “In May, the students release them back into the marshes,” Baldwin said. “There’s a lot of turtles out there that have been named Turtle or Bubbles.”

Closer to Baltimore, I toured two other sites. About 14 miles east of the Inner Harbor, Hart-Miller Island used to be two islands, which probably split from the mainland in the 1700s. Like Poplar, they eroded and are being restored as a single-island wildlife habitat, which will be completed in the next few years. It includes a boat-accessible state park with a sand beach and camping.

Our tour drove by mounds of dredged material, and I was surprised to see that it looks like rocky sand — not mucky, oily and dark, as I’d imagined. Still, some of the material is contaminated by heavy metals that have sunk to the bottom of the bay, so all sites have a rigorous water-testing program to check for pollutants and to make sure that none are being re-released into the water.

Cox Creek and Swan Creek Wetland is near an industrial park at the foot of Baltimore’s Key Bridge. Unlike the other sites, this one includes a dredged material dumping area and an adjacent wetland area that was created to provide habitat for fish, birds and other wildlife.

There isn’t a big demand for tours here, but it’s a hot spot for birders. Nestled between the Constellation Energy and Millennium Chemical power plants, the wetlands offer a scarce haven for wildlife. Walking past four-foot-high cattails, I saw a painted turtle, deer tracks and a great blue heron. I smelled honeysuckle and heard Canada geese honking overhead. On the horizon lurked smokestacks and the giraffelike cranes used to take containers off cargo ships.

Back at Poplar, as we waited on the dock for our boat at the end of the tour, a school group from Easton arrived with two terrapins about to be returned to the wild. One of the students lifted the cover off a white pail, and I saw two hamburger-size creatures crawling around. “What are their names?” I asked.

He looked up, squinting. “They don’t have names,” he said. Then he grabbed the pail, caught up with his classmates and headed out onto the wild island.

Details, Maryland’s rebuilt islands

Kaplan is a freelance writer in Washington. Her Web site is www.melaniedgkaplan.com.