Skip to Main Content

The Mysterious Delmarva Bays: Exploring Maryland’s most unusual wetlands

Eastern tiger salamander; by Mike Burchett

If you look closely at an aerial survey—what scientists call a digital elevation model—of Maryland’s Eastern Shore, you would notice thousands of small, elliptical depressions dotting the landscape like a bad case of chicken pox. The shallow basins are difficult to observe from the ground, and many have been filled in for agricultural use or obscured by new-growth forests.

Nevertheless, these seasonal freshwater wetlands, called Delmarva bays, are integral to the coastal ecosystem and home to a remarkable number of rare or endangered species. For many years, researchers struggled to understand what caused these egg-shaped ponds, which are found along the Atlantic Coastal Plain from New Jersey to Florida.

Mysterious origins
In Georgia, they’re called Grady or Citronelle ponds. In the Carolinas, they’re called, naturally, Carolina bays. On the Delmarva Peninsula, they were once nicknamed Maryland basins, but today are known as Delmarva bays. They are notably smaller than Carolina bays, probably due to the area’s colder temperatures and longer freezes. The name “bay” is a bit of a misnomer, and refers to the type of trees normally found in these wetlands, not to the water within them, which comes and goes. They are most often oriented northwest to southeast along their major axes, with sandy rims along their southeast sides.

Locally, these depressions (which are usually an acre or so in size) were colloquially known as “whale wallows” as it was speculated they were caused by ancient whales beached by the great floods as described in the Bible.

Meadow Beauty (Rhexia); by Ashley Stimpson

One of the earliest formation theories posited that a meteor shower or comet may have created the bays. However, the hypervelocity collisions would have also produced visible destruction and ejection of bedrock. Geologists found neither, thus debunking the hypothesis of an extraterrestrial impact. It was later theorized that the development of subterranean eddies or drainage systems, much like a sinkhole, caused the depressions. This idea, however, does not explain their uniform orientation and shape.

Scientists now believe that Delmarva bays—and their coastal counterparts—were formed by wind blowouts during the Pleistocene Era (2.6 million to 11,700 years ago), when the landscape was vast and wide open. It is thought that wind-driven currents of ponded water elongated the basins and created their characteristic sandy rims.

An irreplaceable refuge
Wayne Tyndall, a restoration ecologist for the Maryland Natural Heritage Program, notes it’s difficult to overstate the ecological importance of Delmarva bays.

“If you could only save one type of wetland, this would be it,” he says. “They have the highest biodiversity conservation value of any wetland type on the peninsula, as they support the greatest total number of plant and animal species, including many that are rare, threatened or endangered.”

Discouraged by flooding and saturated soil, many tree species will not grow in Delmarva bays, creating a meadow-like opening where grasses, sedges, as well as shrubs like buttonbush and sweet pepperbush, can flourish. These open areas are havens for pollinators and migratory birds alike.

Because these seasonal wetlands are geographically isolated and constantly in flux, an incredible number of plant and animal species call these pools home. During dryer years, when predatory fish populations don’t have the opportunity to colonize the waters, amphibians like the endangered eastern tiger salamander thrive. Swollen bladderwort, a floating, carnivorous plant, prospers during wetter years.

Not only do these wetlands provide a sanctuary for rare species, they benefit the land—and the people—around them. Many Delmarva bays are situated near agricultural operations, which typically deposit high levels of nutrients and sediments into the local water. They can reduce those levels by acting as a discharge wetland during the winter and spring, as well as a recharge wetland during the late summer, keeping these nutrient-rich waters from reaching nearby rivers and even the Chesapeake.

Andover Flatwoods; by Ashley Stimpson

See for yourself
Delmarva bays are extremely common on the Eastern Shore, especially in Caroline, Talbot and Queen Anne’s counties, though you may have trouble finding them on your own. Nearly two-thirds of the approximately 17,000 bays have been altered by human activity and often resemble little more than a flooded field.

The Natural Heritage Program is working to reverse that trend. Andover Flatwoods Natural Area was acquired by the state in 1988, and restored to its natural condition. Today, visitors to the area can observe an unusually-shaped Delmarva bay, which from above resembles a long-eared rabbit.

Be sure to tread lightly and avoid wading directly through a Delmarva bay, where rare and endangered species can sometimes be hard to tell from other, less threatened species. Also take the necessary precautions to protect yourself from ticks; they exist in great numbers in these dense wetlands.

No matter what time of year you visit Andover Flatwoods, you’ll marvel at the diversity on display. On spring evenings, the elusive male woodcock takes to the air for his famous, frenzied mating dance. In the summer, the wildflowers pose like supermodels. During the cooler months, you may be lucky enough to spot salamanders racing just below the icy surface, getting ready for mating season.

Other Delmarva bays are open to the public at Bridgetown and Hollingsworth ponds and Millington Wildlife Management Area. A visit to any one of these special wetlands will allow you to appreciate nature’s beautiful ebb and flow—as well as its enduring mystery.


Article by Ashley Stimpson—freelance outdoors writer. Appears in Vol. 21, No. 4 of the Maryland Natural Resource magazine, fall 2018.

Magazine spread promoting subscriptions