MOUNT VERNON, Va. -- Virginia wildlife officials are still trying to figure out why hundreds of snakehead fish made their way up Dogue Creek near Fort Belvoir this weekend.

Some fishermen caught a bounty of snakehead fish over the weekend in the Potomac River tributary. Anglers said they found hundreds of the alien fish Sunday, when the creek was swollen with rain.

Mark Hammond, who has been fishing the Potomac tributary for three decades said it was something he never dreamed he would see.

Hammond said the water was alive. Snakeheads, hundreds of them, were slithering among the minnows, rising up through the concrete blocks that dam Dogue Creek like salmon leaping for freedom.

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Slideshow: Dogue Creek Snakeheads
Slideshow: Snakeheads Found In Little Hunging Creek

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"They're in there by the thousands. You could see them literally coming up along the banks. The ones we caught didn't even put a dent in them," said Hammond, 43, an avid bass fisherman from Florida living here temporarily. "We would throw one in the cooler, two others would jump out and we'd have to chase them through the woods."

Since last year's discovery that the voracious, nonnative northern snakehead had infiltrated the Potomac River and its tributaries, fishermen have pulled them up in ones and twos, each catch a major event that further solidified the proof of an entrenched and breeding population.

In the first half of this year, about 15 snakeheads were caught in the Potomac and its tributaries, including several in Dogue Creek, but nothing has matched the haul Sunday and Monday of at least 80. Its cause isn't yet clear.

"I think we have the state record," Hammond said of the catch behind the trailer lot where he and his friends drink beer and practice bow-hunting.

Nothing was normal about Dogue Creek on Sunday afternoon. The weekend rains had swollen this section, a couple of miles from the Potomac just off Route 1, far beyond its usual thin trickle. The sandy creek bed swarmed with small minnows and bluegills inching upstream toward a marshy pond. Among the smaller fish, Hammond's friend Mike Bowers noticed, were an inordinate number of bass.

"Wait a minute, I thought, those aren't bass," said Bowers, 42, of Mount Vernon. "Those are snakeheads!"

Bowers, Hammond and another friend, Tom Dustin, soon got to work. They didn't need bait. With fishing poles armed with three-pronged hooks, they snagged the snakeheads by the backs. They dipped in nets and pulled out clumps of them. They worked into the evening using headlamps to guide their work, hoping, as they had heard, that someone might be offering a bounty for the predatory species.

"We're trying to get paid," Bowers said.

By Monday afternoon, the ranks of snakehead anglers included Woodrow Minnick, 20, and Matt Thackery, 24, but the catch was declining because the water had subsided.

Still, the brown spotted snakeheads could be seen wending their way upstream through thick blooms of minnows.

"See, see, right there! Right under that tuft in the bank: That's a snakehead," Hammond said, now wielding a long harpoon-like instrument. "There are too many of them. They're here to stay."

The northern snakehead, native to China and Korea, first appeared in the area in 2002, when it was discovered in a pond in Crofton, Md. Authorities found six adults and 1,000 juveniles when the pond was poisoned. Last year came what fisheries experts say is a more disturbing development, when more snakeheads -- with no genetic connection to the Crofton fish -- were found in the Potomac, worrying scientists that the breeding population could throw the ecosystem out of balance.

The Virginia Department of Game and Inland Fisheries has been contacted about the catch but had not visited the fishermen by Monday afternoon to verify the details.

However, a state fisheries biologist confirmed from photographs that the fish are snakeheads, department spokeswoman Julia Dixon said.

"We don't really know how they're going to behave in our waters," Dixon said.

"They're a top-line predator, so they're going to be competing for the same food and space as bass, and we'll just have to see what shakes out," she added.

Virginia fisheries biologist John Odenkirk said 90 snakeheads have been caught in the Potomac and its tributaries, including 70 this year. This is a strong indication that the fish are migrating, because they're moving upstream.

"It's incredible," Odenkirk said.

The catch by Hammond and friends did answer a few questions, such as: Can the snakehead actually walk? Not well. On the ground, the snakehead does stay upright, unlike other fish, but wiggles very slowly across the ground.

Allan Ellis, promotions manager at Bass Pro Shops Outdoor World at Arundel Mills in Hanover, said that although gift certificates of up to $50 were still in effect for bringing in snakeheads, they don't apply in this case.

Only "legal methods," not nets or treble hooks, qualify, he said.

"We're not going to give out $4,000 in gift cards for fish caught in nets," he said. "But thank you for your enthusiasm and thank you for ridding the Potomac of this scourge."