06/22/2012 11:19 pm ET

Dyke Marsh, A Natural Retreat Near Alexandria, Is Shrinking (PHOTOS)

ALEXANDRIA, Va. -- On a recent Sunday morning, Christine Hoskins and George Vargas were among the many people going for a walk along the nature trail at the Dyke Marsh, which is one of the D.C. area's biggest, though rapidly-eroding, tidal wetlands along the Potomac River. Most other visitors had dogs with them, or fishing poles, or binoculars for bird-watching. Hoskins and Vargas were there with their ferrets Rikki and Bells.

"This is a nice place to bring them," said Vargas, watching one of the ferrets leap into some shrubbery. "They really enjoy it."

How long they will get to keep enjoying the marsh is uncertain.

The Smoot Sand and Gravel Company's dredging, from the 1940s until the early 1970s, made the marsh "geologically unstable," according to a report put out by the U.S. Geological Survey in 2011.

The marsh, which the USGS estimates began forming over 500 years ago, has continued to shrink rapidly even since mining stopped, both from human and natural causes. WAMU-FM reported some alarming figures in March:

"In terms of feet of shoreline per year, the current estimate for shoreward erosion is probably 6 to 8 feet a year," says Ron Litwin, a researcher with the U.S. Geological Survey. "Since 2002 to the present, it's an acre and a half a year."

More than a football field's worth of marsh is swept away every year, tree-by-tree, reed-by-reed.

"Now the entire marsh is 53 acres out of an original 183 acres," says Litwin.

Dyke Marsh

When George Washington was surveying the Alexandria area, in the mid-1700s, he said that Dyke Marsh was a "fine improvable marsh." (You can read this quote on an interpretive sign.) The group Friends of Dyke Marsh now estimates Dyke Marsh will be gone in 30 to 40 years due to erosion. Comments on the National Park Service's various proposals for restoring (or not restoring) the marsh were due on Wednesday. Advocates like some of the park service's ideas; the ideas also have detractors.

So the future is rather grim and uncertain. But for now: "This is the best part of my day," said Hoskins. "It's a beautiful morning out here. You get to assemble your thoughts. Watch ferrets enjoy themselves."

Enjoy your own day at Dyke Marsh (driving directions; public transportation directions). Rent canoes, kayaks or sailboats at the Belle Haven Marina. There are some 300 species of birds at Dyke Marsh, and The Friends of Dyke Marsh hold a weekly Sunday morning birdwatching walk. The Northern Virginia Bird Club also sometimes leads guided tours of the marsh -- check the schedule to find out when. Fishing is allowed.