To the hundreds of scientists, conservationists and just plain concerned folks trying to revive the Chesapeake Bay's oyster population, nothing would be more delightful than to be able to plant dozens of signs in the bay warning boats of potentially dangerous oyster reefs.

There was a time, about a century ago, when there was an abundant need for such signs. The bay was filled with mounds of brown, slimy oysters with barnacles and sponges tucked between the shells, and mud crabs, sea worms, and grass shrimp wriggling about. These oyster reefs peeked above the water's surface during low tide, occasionally hampering unwary seafarers but providing a bountiful harvest for the region's fishermen.

The reefs have all but disappeared, but an ongoing push by the state Department of Natural Resources in conjunction with its counterparts in Virginia and Delaware and the Chesapeake Bay Foundation, seeks to reverse this. If they are successful, the rewards could be far more than extra oysters-on-the-half-shell at your local seafood joint.

"In my view, oysters are the most important species, ecologically speaking, in the Chesapeake Bay," said Bill Goldsborough, senior scientist with the Chesapeake Bay Foundation, a nonprofit group of conservationists that works to protect the bay.

This summer, millions of fish have been dying from an overabundance of algae in the bay. Algae hogs oxygen, leaving little for fish to survive on. The ongoing regional drought has exacerbated this by heating the water, creating water temperatures in which algae thrive. It's a big problem for fish but a welcome one for oysters: They love to dine on algae.

Oysters once played a crucial role in the fragile Chesapeake Bay ecosystem by keeping the algae population in check, ensuring a plentiful oxygen supply for other bay denizens. But that was before overfishing and a series of diseases devastated the population. Today, only 1 percent of the number of oysters available at the turn of the century remains.

The Oyster Recovery Program aims to get the oyster population to at least 10 percent of what it once was. Some ecologists hope to get it up to 50 percent. The most innovative aspect of the program focuses on "replanting" oysters in the reef formations that once were common. Over the last two years, the department has purchased more than 5,000 bushels of oysters from fishermen for replanting.

In addition, armies of volunteers are growing oysters at home and then planting them in the bay at maturity, hoping they will reproduce. Groups including the U.S Naval Academy, Potomac Electric Power Co. and bay area schools have volunteers participating in the effort.

Creating the new oyster reefs is something of an art. Barges haul the oysters to the outer edges of sandbars, where the water depth is about 10 feet. The oysters are piled onto the barge and are forced into the water using a water cannon. This makes it easier to ensure that the oysters end up in a pyramid-like pile.

The shape of the pile is crucial to the success of the project. A pyramid shape--as opposed to a flat oyster bed-- creates nooks where oyster larvae can hide from predators such as crabs, increasing the likelihood that oyster progeny will mature.

A reef formation also gets oysters closer to the surface, where oxygen tends to be lowest and the algae population highest. Oysters near the surface can spend their days feasting rather than trying to pump sediment out of their gills half the time--the lot of oysters who dwell on the bay's floor. The growth and reproduction rates of oysters close to the surface tends to be higher.

Given a year, a pile of mature oysters can develop into a healthy oyster reef, a thriving mini-ecosystem that attracts crabs, shrimp, rockfish, trout and dozens of other bay creatures. This may seem like the clever invention of biologists, but the oysters deserve proper credit: They have been living in reef formations for hundreds of years. It was only in this century, when millions of people realized the pleasures of a raw oyster with a dash of hot sauce, that the reefs disappeared.

"Think of Florida without its reefs. That's what the bay is like without oysters," Goldsborough said.