The latest northern snakehead fish found in the Potomac River may be the most significant yet: It's a baby, three inches long and proof that the Asian predator is breeding in native waters, scientists say.

With the discovery last week in Alexandria, biologists now confront a scenario that was considered a kind of ecological nightmare. The snakehead, they said, will be nearly impossible to eradicate and could drive out other Potomac wildlife, even threatening the river's plentiful bass population.

"The snakeheads are in charge," said Walter R. Courtenay Jr., an expert with the U.S. Geological Survey.

The northern snakehead, a native of China and Korea, is a voracious predator that can grow several feet long. It first gained notoriety in this area in 2002, when a pair were discovered in a Crofton pond, along with thousands of young. The pond was poisoned to kill the fish.

The species reappeared in force this summer, as anglers caught 19 adult snakeheads in the Potomac and its tributaries. Scientists aren't sure where the first Potomac snakeheads came from but say it's likely that they were imported for food or as aquarium fish and then dumped.

As the summer went on, each new catch made it more likely that the fish was here to stay, scientists said. But they held out hope because, despite weeks of intense searching with electro-shocking equipment, no juvenile snakeheads had been found.

That changed Wednesday, when Alexandria resident Jack Ferris noticed a fish flopping around in a clump of hydrilla -- an underwater grass -- at his subdivision's boat ramp on Dogue Creek.

Someone else at the ramp said it was a minnow, but Ferris, 58, thought he recognized the small gray-green fish as something else.

"That is a spittin' image" of an adult snakehead, Ferris remembered thinking. "But it's just a mini."

Ferris took the fish, which he nicknamed Skippy, home in a Gatorade bottle and called Virginia authorities.

On Friday, it was confirmed: Skippy was a snakehead probably born this summer in Dogue Creek, a Potomac tributary that has yielded a concentration of the fish, according to the Virginia Department of Game and Inland Fisheries.

Knowing that snakeheads lay a massive amount of eggs, scientists reasoned that there are likely hundreds or thousands more juvenile fish in the river.

"Eradication, then, is not going to happen," said Julia Dixon, a spokeswoman for the Virginia agency. "We're going to have to manage them."

In the short term, both Maryland and Virginia authorities said the new discovery would not alter their efforts against the snakehead.

One of their strategies: After the underwater grasses recede in cold weather, Maryland authorities plan to sweep through the shallows with huge nets, trying to catch more of the youngest generation.

The snakehead is not the first nonnative species to invade the Potomac; before it came the blue catfish; the carp; even hydrilla grass, another Asia native.

But officials in both states conceded that this new predator might have serious effects that might not be fully realized for a decade or more.

"There's only so much room out there for so many fish," said Steve Early, a biologist with the Maryland Department of Natural Resources. "You're probably going to displace something."

Many worry that the snakehead's victims might include the largemouth bass. The Potomac is known nationally as a bass fishery, with about 60 fishing tournaments a year in Charles County alone.

Fishermen buy gas and food and stay in hotels in communities along the river, said Joanne Roland, Charles County's director of tourism. Each of the larger televised tournaments, with about 400 anglers, contributes about $250,000 to the local economy, she said.

"This is one of the top five bass fisheries in the country. It is not just another fishing hole," said Steve Chaconas, 48, of Stratford Landing, who guides bass fishing trips on the Potomac. "When you have an invasive species, it really throws the whole food chain out of balance."

The problem, he said, would not stem from adult snakeheads squaring off against adult bass but from snakeheads preying on the zooplankton and smaller fish, such as shad and perch, that young bass need for sustenance.

"If you're a fisherman, I think eventually you will notice the difference," Chaconas said. "This will disturb the food chain. This will cause problems."

A three-inch northern snakehead was found last week in Dogue Creek, a Potomac River tributary in Virginia.