As buckets of thrashing, iridescent herring were hoisted out of the water, Maryland state biologist Jay O'Dell turned on his video camera, like a proud father at a graduation.

Ten-inch blueback herring were spawning by the hundreds at the base of the Patuxent River's Fort Meade dam. Caught in nets and transferred to a waiting tank truck, they soon were to become pioneers in a fish rite of passage orchestrated by O'Dell for the Maryland Department of Natural Resources.

The offspring of this year's spawning, expected back in these parts in four to five years, will be the first generation of migrating fish to swim to some Maryland waters, such as the upper reaches of the Patapsco River, in 150 years. Shad and herring once were so abundant in the tributaries of the Chesapeake Bay that old-timers used to jest that you could walk across the river on them in spring.

"But since the Industrial Revolution, they've been building dams blocking spawning migration and closing off habitats," O'Dell said. " . . . There has been a real dramatic decline in anadromous {migrating} fish throughout the Chesapeake Bay area. It's been apparent since the turn of the century."

O'Dell knows the prospects for anadromous fish reproduction better than just about anyone else in Maryland. A former biology teacher at Howard County's Atholton High School, he spent 16 years finding the hundreds of culverts and dams and roads that thwart fish migration along Maryland's 46 tributaries to the Chesapeake Bay.

Now, based in large part on O'Dell's field research, Maryland is undertaking an ambitious effort to install 24 fish ladders or other passages to unblock historic spawning waters for fish such as river herring. The state is the first jurisdiction in the Chesapeake region to make good on a 1987 agreement to clear the way for fish.

"It's ecologically valuable to have spawning fish" that are food for other fish, said Howard King, program chief with the state fisheries division. Also, he said, "herring and shad offer sport fishing and commerical fishing opportunities."

Small herring are eaten by smallmouth bass and striped bass, the rockfish so important to commercial fishing in the region.

Blueback herring, among the type of fish that live in salty coastal areas but swim to fresh water in the spring to spawn, have made their annual trek from waters off New England.

Some 25,000 to 30,000 herring netted at remaining spawning waters at Fort Meade and on the Eastern Shore have been trucked to stretches of Maryland rivers that haven't seen spawning migratory fish in generations. One female herring can produce 50,000 to 100,000 eggs, less than half of which will survive, O'Dell said.

Herring and shad, also transported for stocking this year, once spawned in the Patapsco as far north as Sykesville, where the north and south branches of the river meet, O'Dell said. "But shad runs ended in the Patapsco in the 1930s, and those were only to the vicinity of Elkridge," he said.

Now, the state is planning to provide passage at four dams that block access to about 22 miles on the Patapsco from Elkridge to north of Ellicott City, and on two Patapsco tributaries. Statewide, the fish passage program is expected to cost several million dollars.

King said officials also plan a "new, improved fish ladder" at Little Falls on the Potomac, which is much larger than the Patapsco and thus capable of supporting more fish.

Officials hope the herring will spawn offspring that will become genetically conditioned to return to these waters in about five years, when the rivers should be open to passage.

Of particular interest to state environmental officials is the Patapsco, so polluted with industrial and municipal discharges 15 to 20 years ago that "it ran different colors every week," O'Dell said.

With sewerage systems in place and industries such as paper and textile mills forced to clean up their acts, the Patapsco is so improved that bass have become more abundant.

Maryland owns much of the land bordering the river and can protect the watershed, King said.

And now sediment in the river is "relatively clean of industrial contaminants," he said.

Since last year, Maryland has even resumed stocking the Patapsco with a delicate bellwether of the state of the environment: trout.

Recently, O'Dell was holding forth in a parking lot near the Bloede Dam in Patapsco Valley State Park, describing the state's efforts to restore the river. As if cued by a director, a fisherman trudged up to a nearby car, carrying a string of three good-sized rainbow trout.

"Here comes a man with some trout which he just caught over in the Patapsco River," O'Dell announced, rushing over to take photographs for his frequent slide presentations. "Twenty years ago, you couldn't have caught anything."

In opening the river to fish passage, "we're writing a new chapter in the history of the Patapsco River valley," O'Dell told officials this spring at a ceremony at Oella, where Torrey Brown, state natural resources secretary, and others dumped ceremonial buckets of herring into the river.

"We've quit putting chemical and dirt and runoff into it. And we're paying attention by not building in the flood plain," Brown said. "If we can do this here, we know we can do it everywhere."

With Brown were representatives of the Chesapeake Bay Foundation and the National Fish and Wildlife Foundation, which are augmenting the state funding for the restoration program.