It’s a minor miracle that happens every year about this time: Driven by an urge to spawn, great schools of American shad swim from feeding grounds in the Atlantic Ocean to the Chesapeake Bay, sensing their way back to the rivers where they had been born three years earlier.

But what happens once they arrive is not as awe-inspiring. The shad queue up for what can be described as a Chesapeake Bay version of the TV show “Wipeout,” on which contestants have little chance of surviving ridiculously tough obstacles placed before the finish line. The shad are often pushed off course by powerful water flows from hydroelectric dams, cut up by turbines and bewildered by fish elevators that lure them into a gate, lock them in and lift them in a bucket over the dam.

In recent years, the silvery shad that Native Americans used to teach European settlers how to fertilize crops, that helped feed George Washington’s Continental Army, and that provide food to eagles and otters, have started to disappear in alarming numbers. The disappearance has started talk of extinction, mostly because of four giant dams that block the Susquehanna River in Pennsylvania, where the fish were once abundant, according to the U.S. Fish and Wildlife Service.

Biologists say there’s one ray of hope for efforts to restore the Susquehanna’s shad — the looming expiration of operating licenses for two of the dams. Before granting a 30-year renewal, the Federal Energy Regulatory Commission requires the dam operators to study the environmental effects of their facilities. Based on the findings, the commission can require that conditions be greatly improved so that more shad can swim past them.

“It all depends on FERC,” said Mike Hendricks, a longtime fisheries biologist for the Pennsylvania Fish and Boat Commission, which operates a shad hatchery. It “needs to tell the dams to have 80 to 85 percent passage of the shad. If we can get [it] to do what needs to be done, we can get restoration. If we can’t, the game’s over.”

The commission confirmed in a statement that two dams, the Conowingo Hydroelectric Plant, built in 1928 and run by Exelon Power, and the York Haven Hydroelectric Dam, built in 1910 and run by York Haven Power, are in the “pre-filing state of the relicensing process,” meaning they must conduct environmental impact studies of the shad and other species affected by the plants.

A decision is a ways off, with release of the studies, critiques and public comments pending over the next three years.

Research shows that only 33 percent of shad get by the Conowingo dam and only 8 percent make it past York Haven, said Hendricks, citing figures provided by Pennsylvania.

Another dam, the Holtwood Hydroelectric Dam, owned by Pennsylvania Power & Light, passes 26 percent of shad. The Safe Harbor Hydroelectric Station, run by Constellation Energy, allows 72 percent of shad to pass.

Going with the flow

Water flow is like a road for shad. They swim against a current to head north. If the flow is too weak, they meander. If it’s too strong, they look for a milder passage, Hendricks said. The Conowingo dam often releases 85,000 cubic feet of water, far more than the 500 cubic feet of flow sought by shad.

With its high passage rate, Safe Harbor, which produces enough power to serve 250,000 homes, is praised by environmentalists, Hendricks said. But the cost of helping shad is not cheap. Safe Harbor’s fish lift cost nearly $20 million to build and $134,000 to operate each year, said Juan Kimble, the dam’s president and chief executive.

In 2001, only 200,000 adult shad were counted in the fish elevator at the Conowingo dam, the first plant they encounter on their swim up-river. Last year, that number fell to about 37,000.

“We’re losing this icon, a connection to our past, and our future,” said Mark Bryer, director of the Chesapeake Bay program for the Nature Conservancy. “The spawning run of this fish is a harbinger of spring for us.”

Restoring the shad population is important because they were “historically an economic force,” Bryer said. “This fish is . . . our salmon of the East.”

The U.S. Fish and Wildlife Service, the Virginia Department of Game and Inland Fisheries, the Maryland Department of Natural Resources and the D.C. Department of the Environment are trying to help restore the shad.

To increase the shad population over the years — as shad struggled to get past the dams in the Susquehanna — hatcheries entered into contracts with some agencies to catch them, extract a few eggs, fertilize them and taxi them north by truck to their final destination, about 100 fish per load.

But that doesn’t always go smoothly. First, trucking shad to rivers is expensive, Hendricks said. Second, they don’t have enough trucks to make up for all the shad being lost. “We’d need 20,000 truck loads,” Hendricks said.

Third, Mother Nature is fickle.

Last week, Ian Park, a Fish and Wildlife Service biologist, felt the frustration of things going wrong. Weeks of heavy rains made it harder to catch shad. He roared out on the river in the black of night Tuesday, knowing that it would be a hard fishing trip.

Park and his team of five recent college graduates threw out 10 gill nets from two boats in 44 feet of water, waited 45 minutes and pulled in almost nothing, except for catfish and gizzard shad, a similar, slightly uglier variety.

After two hours, Park and two helpers caught only two American shad males that were ready to spawn. The other boat caught only three females that were ripe with eggs. The workers combined their paltry catch.

Park slid a thumb and forefinger across the bellies of the fish and out came eggs and sperm. He whisked and stirred the eggs as if he were about to bake a cake.

The shad, stressed out by the net and the stomach pump, died in Park’s hands. This almost always happens, Park said, but their lives are sacrificed to create hundreds of thousands of fish in Pennsylvania.

But probably not this year.

“Our best night last year was 53 liters, an entire trash can full of shad eggs,” Park said. “This year our best night was 21. Last night, we had 91 / 2 liters. Not exactly a good night.”

While the shad were giving their lives for science, Park and his workers were risking theirs. Under a half-moon, on flat water, with boats zipping back and forth in the dark, Park worried about being struck by another boat.

The Fish and Wildlife Service is in the final year of a three-year, $100,000 contract to harvest shad eggs for the Pennsylvania Fish and Boat Commission’s Van Dyke Hatchery. The hatchery fertilizes the eggs, which are then seeded in the state’s depleted rivers.

The Potomac, which has smaller dams than the Susquehanna, has healthier shad populations. Still, seeding this year isn’t going well, because rainfall has increased water flows, confusing the shad.

In the end, the shad caught Tuesday would do nothing to populate the Susquehanna. The eggs weren’t nearly enough to truck 200 miles to the hatchery near Lewistown, Pa. Park fertilized the eggs and released them into the Potomac.