Light shimmers through the trees and scatters on the surface of the Delaware River's back channel.

About 45 of us have crossed a two-lane bridge from the mainland, cleared security, and parked on Petty's Island.

"Welcome to Acquikanasara," tour guide Bob Shinn says, launching the vivid volley of vowels in the Lenape name for this place.

There's anticipation, as well as the unmistakable aroma of autumn, in the air; the private island we stand upon has pretty much been closed to the public for 100 years.

"It has a lot of mystery to it," Camden resident Mike Morgan observes.

Like most of us, Morgan has never set foot on these 400 acres, which are shaped a bit like Delaware and hug the eastern riverbank where Camden meets Pennsauken.

"I've been wanting to get out here forever," says Olga Pomar, who heads up South Jersey Legal Services Inc.

The organization was involved in a fierce legal battle against a redevelopment proposal encompassing Petty's Island, Pennsauken's riverfront, and adjacent sections of Camden a decade ago.

The plans for upscale housing and golf course projects finally sputtered out in the 2007 real estate crash.

"This is a victory walk, because the island will be preserved," says Mike Hagan, who would have lost his home in Camden's Cramer Hill section to eminent domain had developer Cherokee succeeded.

Our group heads south along a well-maintained trail on Petty's eastern perimeter. A mile and a half ahead lies the island's southern tip, where we'll turn around; only about 80 acres are open for tours.

"We're trying to garner support for historic preservation and watershed conservation, and build awareness," says Kelly Wenzel, an education coordinator with New Jersey Audubon.

Although half of the island has been altered by industrial activities, eventually "it will be a wildlife sanctuary, a park with trails people can enjoy," Wenzel adds.

She led the tour along with Shinn, who represented the Cooper River Watershed Association and Camden County Historical Society. Many of Saturday's visitors were members of South Jersey environmental, historical, and civic organizations.

New Jersey Audubon oversees these monthly public visits and twice-yearly cleanups for the New Jersey Natural Lands Trust. The trust was granted a conservation easement by Citgo, the Venezuela-based oil company that owns the island and promised in 2009 to donate it to New Jersey.

Citgo also has promised $3 million for environmental remediation and construction of a visitor center by 2020.

While the company has ceased operations on the island, a marine terminal - Crowley Liner Services Inc. - employs about 90 people there. Its lease expires in 2017.

"Ultimately, we're going to have a wonderful wildlife preserve in an urban area," Shinn says. "It will be accessible to families who ordinarily wouldn't get a chance to go to such places."

As we walk, dense foliage and an embankment shield oil tanks and the marine terminal parking area from our view. A white-tailed deer bounds into and out of view; foxes and groundhogs also call the island home, as do egrets and herons.

We reach our destination, and many in the group clamber down a 15-foot embankment to a stony beach. The Ben Franklin Bridge and the Philadelphia skyline rise in the distance, across the silvery river, and I realize I've never seen them in quite this light before.

"What amazes me is how people react," Shinn says. "It's like opening the doors to a secret gem."