Young oysters are growing naturally on an old bed in the South River, rather than being planted there by state workers.
The discovery, on an oyster bar near the mouth of Selby Bay, has renewed environmentalists' hopes that the ailing Chesapeake Bay shellfish population may be starting to recover.
"That's in an area where you wouldn't expect to get a lot of natural reproduction," said William J. Goldsborough, a fisheries scientist with the Chesapeake Bay Foundation. "I would say it's certainly significant. If you have reproduction, more than likely it is not limited to one bar."
Similarly, John Flood, who heads the Federation of South River Associations, was enthusiastic, saying he viewed the oyster spawning and the return of patches of seaweed as early signs the river's health was rebounding.
But state officials did not find these sparse young oysters particularly significant.
"In the past five years, there has been some spawning," said W. Peter Jensen, director of fisheries for the Maryland Department of Natural Resources (DNR). But the bar is "not on an upswing," he said.
"I think it's probably been this way for a long time. This one probably is real stable," he said.
The find was made in January by DNR fisheries scientists who were surveying the 194-acre natural oyster bar.
The oyster bar was last seeded by the state in 1989, and most of those oysteres probably were harvested. No spat was found anywhere in the South River in 1991, according to the DNR report of the survey.
Mr. Jensen said his agency knew the bar had some hard shell bottom for oysters to grow on, though most of it is mud or sand.
"Natural oyster bars are somewhat cyclic. Under the right conditions, you will have some spawning," he said.
In the last few years, the river's salinity has increased, making the water more hospitable to oysters, he said. In addition, patches of seaweed have returned to areas that have been barren for decades, a sign the water quality is improving.
Nevertheless, the bar is hardly in optimal condition. Live oysters were found on only about 7.7 acres of the 115.5 acres surveyed. Its sparse oysters place the bar in the lower 10 percent of 40 natural oyster bars in the Chesapeake, according to the DNR report.