Hunting for sunken treasure evokes a sense of mystery. On a cold day in early February, there was plenty.

A misty rain chilled to the bone as Pete Springer guided his skiff past a rusting hulk, part of the Potomac River’s abandoned “ghost fleet” in Mallows Bay. Dense fog closed in, obscuring the wreck, shoreline, and most everything more than a few yards ahead. Only the GPS kept the boat safely headed downriver.

Springer, accompanied by Marty Gary of the Potomac River Fisheries Commission, was seeking something precious in the Chesapeake Bay region — a trove of oyster shells said to blanket the river bottom in an area where bivalves haven’t lived for quite a while. Exactly how long, no one seems to know.

The “great shellfish bay,” as the Chesapeake was known in earlier times, now suffers a severe shortage of both oysters and their shells. Historically, Bay oysters grew on great reefs made of older shells, and those shells are now in demand both for aquaculture and oyster restoration projects.

Nautical charts of the Potomac show about 30 “lumps” or knolls in a 10-mile stretch above the U.S. 301 bridge. That prompted speculation, as underwater hills in the Upper Bay mark one-time oyster reefs now smothered under thick layers of silt and sand.

Last summer, fisheries scientists sampled nearly half of the submerged knolls in the upper Potomac. They hit the jackpot, sort of. Every haul of the dredge came up full of shells — but no live oysters.

On that murky February morning, Springer, a waterman who oysters downriver, likewise struck paydirt when he dropped hand tongs over the side of his skiff where the GPS showed a lump.

“Hear that?” he said, as the tongs’ steel jaws produced clinking sounds from beneath the water. “There’s plenty of shells here.”

After repeated tries under tricky conditions, Springer finally pulled some aboard, festooned with bits of brown grass and encrusted with dead barnacles.

Marty Gary of the Potomac River Fisheries Commission examines a handful of oyster shells tonged from the river by waterman Pete Springer. Credit: Dave Harp / Bay Journal Media

Chris Judy, shellfish division director for the Maryland Department of Natural Resources, estimates that the 13 lumps he helped sample last summer contain 750,000 bushels of the shell. If other lumps are similar, he said the total could be 1 million bushels.

The discovery of such an extensive shell deposit raises questions about how the river has changed over time. The water where the shells are located is practically fresh, with salinity levels that periodically dip too low for oysters to survive for long, much less reproduce. When did oysters flourish there, when did they die out, and why?

It’s also stirred interest in dredging those shells for use elsewhere. There’s a clamor for oyster shells among watermen, who see them as crucial to maintaining and rebuilding the Bay’s wild oyster fishery. Oyster farmers working leased patches of the bottom also are desperate for shells on which juvenile oysters can grow. Government agencies and nonprofit groups working to restore the Bay’s depleted oyster population for ecological benefits want a shell for that effort, too.

“Shell is in short supply, and it’s expensive,” said Gary, executive secretary of the Potomac River Fisheries Commission. The eight-person panel, with members from Maryland and Virginia, regulates fishing in the Potomac from the Bay to the District of Columbia.

Gary said that lately he’s been unable to buy shell at any price. It’s preventing the commission from replenishing oyster-bearing reefs in the lower Potomac.

Shell to shell

Oysters produce their own shells. But to reproduce, their larvae need to attach to something hard, typically the shell of a live or dead oyster. Over eons, oyster larvae settled atop the shells of old oysters, building reefs in the Chesapeake and its rivers.

Today’s population is a shadow of what it was 150 years ago, historically overharvested and ravaged for decades by diseases. With fewer oysters to replenish them, sediment washing off the land buried many reefs, preventing new oyster larvae from finding homes.

Theoretically, those old shells could be reclaimed, but it’s costly and often controversial. The Department of Natural Resources worked for years to get a permit from the U.S. Army Corps of Engineers to dredge 5 million bushels from Man o’ War Shoal, a massive fossil shell deposit near the Patapsco River’s mouth. But recreational anglers, environmentalists, and even some watermen fought it, arguing that dredging would hurt water quality and degrade reef habitat for finfish. The state’s Board of Public Works has not authorized the project.

Frustrated, watermen have urged Maryland to go after other shell deposits. One bill in this year’s General Assembly would direct DNR to seek permits to dredge old shells from 27 locations, including the Potomac River. Another bill calls for a survey of Bay and river bottoms to better identify buried shell deposits.

Because oyster shells are in short supply, clamshells and granite have been used in the five large-scale oyster restoration projects Maryland has committed to under the 2014 Chesapeake Bay Watershed Agreement. Surveys have found hatchery-spawned oysters survived and reproduced on those substitutes, sometimes better than they have on an oyster shells.

But shells are greatly preferred as substrate, especially by watermen, even when the reefs being created or enhanced are in a sanctuary.

Several years ago, DNR estimated that the Potomac harbors 34 million bushels of old shells. That’s second in volume only to estimates of Man o’ War’s buried bounty, up to 100 million bushels.

Waterman Pete Springer lifts a tong load of oyster shell from the Potomac River. Credit: Dave Harp

But the shells in the upper Potomac are different from many other old reefs because they are not covered by silt and sand. They wouldn’t require hydraulic dredging, the usual method for extracting buried shell deposits, which stirs up the bottom and clouds the water.

Their unusual condition and location have raised scientific interest. For those same reasons, some environmentalists caution against disturbing them.

“It’s a very inhospitable place for oysters,” said DNR’s Judy, because the water is generally too fresh. Oysters need at least a little salt, 10 parts per thousand or more, to survive and reproduce.

Monitoring from the 1960s through the mid-1980s shows that salinity at Maryland Point, the upper reach of the shell lumps, averaged between less than 1 ppt and a little more than 7 ppt. U.S. Geological Survey data going back to 1985 show salinity rarely got higher than 10 ppt and several freshets pushed levels close to zero in spring and summer, critical times for oysters to feed and reproduce.

Judging from the generally small size of the shells — many not much bigger than a quarter — Judy said the oysters either didn’t live long or didn’t have favorable growing conditions. Yet, given how completely the lumps are covered, he suggested the oysters must have been living and occasionally reproducing there for a long time, perhaps a century or more.

When Europeans first settled the region, brackish water reached farther upriver, said Claire Buchanan, a scientist with the Interstate Commission on the Potomac River Basin. But after the 1700s, she said, forest removal and farming practices led to rampant soil erosion, and the deluge of sediment altered the shape and volume of the Potomac, pushing saltier water downriver.

Others think the upper Potomac shells are more recent. Roger Mann, a shellfish researcher at the Virginia Institute of Marine Science, told a committee of the Potomac fisheries commission that they were likely several decades, not centuries, old.

Springer, 48, said he knew oyster shells were in that area because he and his father used to fish there and pull some up in their gill net.

A few older watermen recall tonging for oysters that far upriver or hearing of it decades ago. But in 1972, Tropical Storm Agnes flooded the Bay and its tributaries with muddy freshwater, killing most oysters in the Potomac. Afterward, the only oysters that far upriver were on a single reef near the lumps — until 2019, when record rainfall wiped out the last survivors.

Use them or leave them?

If conditions in the upper Potomac are unlikely to allow oysters to come back, watermen and some fisheries commission members wonder if they could put those shells to better use by moving them downriver to enhance active reefs in saltier areas.

“I say if they’re there, take them and do something with them,” Springer said, “because they’re not doing anything up here.”

But there are hurdles to tapping those shell lumps. Part of the area is an oyster sanctuary, and much of it also is a spawning reach for striped bass, which supports a valuable commercial and recreational fishery.

The Potomac is also deemed critical habitat for Atlantic sturgeon, which is protected from disturbance under the federal Endangered Species Act. Endangered shortnose sturgeon have also been caught in that area.

Tom Miller, director of the Chesapeake Biological Laboratory of the University of Maryland Center for Environmental Science, said that to reproduce successfully, sturgeon need clean, hard river bottom to lay their eggs. That’s the kind of habitat those shell lumps appear to present, he pointed out.

“This is a resource that’s in very, very short supply, and the benefits of having access to 700,000 bushels of it are clear to all,” Miller said during a fisheries commission committee meeting in January. “The challenge we face is that the costs aren’t [clear]. I don’t think we fully understand what [oyster reef] ecosystems are and what role they play.”

Marty Gary of the Potomac River Fisheries Commission checks coordinates with waterman Peter Springer to locate mounds of oyster shell in the Potomac River. Credit: Dave Harp / Bay Journal Media

Allison Colden, Maryland senior fisheries scientist with the Chesapeake Bay Foundation, suggested leaving the shell where it is, at least until it’s been thoroughly studied.

“Obviously,” she said, “it reflects a time when the hydrology of the waters of the Potomac and the Chesapeake Bay [were different enough] to have oysters reproducing and depositing shell that far up the river.” As such, she said, the shell-covered knolls are unique.

“This is a nonrenewable resource,” she said. “As soon as we remove it, it’s not coming back.”

Further complicating the situation: Maryland owns the river bottom, so the state — not the fisheries commission — gets to decide what to do with the shells.

But DNR’s Judy told some members of the commission that state officials would consider a pilot project that would skim shells off the tops of a few lumps. That’s the only way to gauge the environmental impacts, he said.

The issue will come up for discussion on March 10 at the quarterly meeting of the fisheries commission. If the panel wants to go ahead, Gary said he’d work with the advisory committee to develop options to submit to DNR, then to state and federal permitting agencies. It could take a year or longer, he said, but given the unknowns and complexity, there are good reasons to proceed deliberately.

“What’s important now is they’re there,” Judy said. “Is there a way to potentially use them? Or is it best to leave them where they are?”

This article was originally published on

Tim Wheeler is the Bay Journal's associate editor and senior writer, based in Maryland. You can reach him at 410-409-3469 or

Leave a comment

Leave a Reply