It came from the Potomac: even snakeheads have a lobbylist.

In Snakehead Terror, a low-budget horror movie broadcast earlier this year on the Sci Fi Channel, the residents of a small Maryland fishing town found themselves plagued by a species of fish accidentally transplanted from China: Channa micropeltes, otherwise known as the snakehead. In the fictional infestation's early stages, the green-skinned fish were merely a nuisance, and local authorities poisoned the town's lake in hopes of eradicating the pesky saw-toothed beast. But the poison did its trick a little too well and killed off most of the lake's other inhabitants along with--or so it seems--the snakeheads. Two years later, a desperate entrepreneur dosed the water with human growth hormone, aiming to revive the local fishing economy. Any 6-year-old with a television set can guess what happened next: It turned out that not all the snakeheads were eradicated, and the survivors returned with appetites matching their newfound dimensions.

Unlike most of what's shown on the Sci Fi Channel, the plot of Snakehead Terror edges uncomfortably close to reality. Two summers ago, the snakehead--a hardy, aggressive species that dates hack to the Paleozoic era and can survive for a time outside of water began to turn up in ponds in Wisconsin and Maryland, devouring plants, other fish, and even small mammals. A few pet owners had acquired the snakeheads as exotic pets and then, apparently had second thoughts. The Washington Post interviewed one such man, Louis Galeano: "Galeano bought four snakeheads from a pet shop in Waldorf [Va.]," the Post reported, "kept them in a 35-gallon tank, and fed them 20 plump goldfish twice a week. They grew like Godzilla, he said, and mealtime became a slaughter. He wouldn't put his hand near the water ... 'They scare me,' he said. 'They just kill and cat and eat and kill.'" After three months, he took the snakeheads to the pet store. Other snakehead owners were less scrupulous and apparently just dumped them into the nearest body of water. Worried about an infestation, local environmental agencies dispatched task forces to places where the fish had turned up. They drained some ponds, poisoned others, and in some cases used electric shocks to stun the fish and bring them up to the surface.

But, as in the movie version, not all the snakeheads were -killed. Last month, an angler fishing for bass in a tributary of the Potomac River, just a few miles south of the monuments on D.C.'s waterfront, caught a 10-pound snakehead that thrashed so hard he thought he was fighting a 25-pound fish. Several more specimens have since been discovered in other nooks and inlets of the sprawling, brackish river. This infestation has authorities concerned. Because the Potomac is too big for shocks or poisons to be practical, biologists worry that the snakeheads will continue to breed and spread.

Snakeheads aren't the only invasive species wreaking havoc in the United States. Other harmful organisms--bugs that destroy crops, alien fungi that cat trees, and other ecosystem-destroying fish--infiltrate our borders regularly. Such invasive species, according to one Cornell University study, cost the American economy as much as $138 billion annually by damaging natural resources and agriculture production. Some are already on the Environmental Protection Agency's list of banned species and make it through anyway in the suitcases of unscrupulous importers or the under-inspected bilges of commercial ships. But many exotic species are imported legally by pet shops and exotic food stores because of an oddity of the law. Under current statute, the government can only ban a species after it has already caused substantial ecological damage. Thus, environmentalists have lately pushed to replace this system with a "clean list" strategy, under which importers would be required to prove that foreign species are safe before importing them. (Australia and New Zealand both adopted "clean lists" during the 1990s, and have seen their costs from invasive damage plummet.)

But any effort to staunch the flow of new invasive species is liable to face an uphill fight. In Washington, the most sensible-seeming legislation must fight through the tangle of organized interest groups, the most arcane trade has its own membership organization with lobbyists on start, and even a foot-long prehistoric garbage truck has its defenders.

The Pet Industry Joint Advisory Council is headquartered in a sprawling, big-windowed, glass-and-brick office building in downtown Washington. On a hot Sunday afternoon last month, I paid a visit there to Marshall Meyers, the group's executive director and a self-styled intellectual--his shelves are crammed full of books on Middle Eastern history. We sat at a long oak table in the conference room, which. was decorated With a large oil painting of a Kimodo Dragon perched on a rock, its forked tongue lashing somewhat creepily behind Meyers. The building's air conditioning didn't seem to be working properly, and Meyers, a tall, heavyset man, was sweating profusely--probably from the heat, but perhaps from the Sisyphean task of arguing against any effort by the federal government to ban these vicious killer fish.

There's no definitive proof, he told me, to support the charges in the popular press that snakeheads had been released into the wild by frightened owners and therefore, he said, pet shops and importers may be entirely innocent. "It's a knee-jerk reaction to blame the aquarium industry," Meyers said. Instead, he speculates, the fish in the Potomac may have been dumped there by a few unscrupulous individuals who had been breeding them locally: "I suspect snakeheads have been in these waters for a long, long time."

This was an artful dodge. There is zero evidence that snakeheads had been in the wild here until very recently, and even if some were breeding them domestically, the stocks must originally have derived from China. Didn't it make sense, I asked, to move to a clean list system that would ban the import of potentially dangerous creatures like snakeheads?

Meyers leaned back and smiled broadly, then pounced. "The problem with clean lists is how can you block all invasives when you don't fundamentally know what invasives are?" he asked. "The science isn't there yet."

The regions of the United States are so ecologically diverse, he continued, that plants and animals that are native to, say, the bayou s of Louisiana may be very damaging to local environments in the northern Rocky Mountains. So where should one draw the line? Should it be illegal for Pacific Northwest oyster farmers to raise, as they do now, species of oysters that originated off the coast of South Carolina?

Another artful dodge. While it may be theoretically possible for a domestic species to migrate and cause substantial economic damage elsewhere in the United States, the pet industry cannot point to a single example of this ever happening.

Having tried to attack the science, Meyers then attempted what might be called the Rush Limbaugh defense. Just like the famed talk-show host once blamed the press for going easy on the on-field performance of Philadelphia Eagles' quarterback Donovan McNabb because of his race, Meyers accused environmentalists who support clean lists of failing to point the finger at the real perpetrators. "Critics are afraid to address the ethnic side," Meyers told me. "You're not going to find snakeheads at your average pet store. But it's politically incorrect to say it's in the Asian live food market. These things are being flown in daily from China." And, indeed, such markets are widespread: Undercover agents have obtained snakehead specimens from Asian live food vendors in New York, Houston, Orlando, St. Louis, and other cities.

In recent months, 15 states and the District of Columbia have made it illegal to own or import snakeheads. But it will probably take a federal ban and federal inspectors to stop trafficking.

After speaking with Meyers, I tracked down an Asian live fish market located in a small grocery store in Washington's Chinatown. There were no snakeheads advertised as such in this market, but I discovered a tank labeled "China Catfish" that matched photos and descriptions of what I was looking for. The proprietor ignored my question about whether this was in fact a snakehead, insisting it was a "very special fish," and that this was all I really needed to know. There was nothing to stop me from buying this "very special fish," driving down to the Potomac, and feeding the snakehead terror in the Washington region. Instead, I bought a pound of fresh tuna and headed home.

Eric Pfeiffer writes for National Journal's Hotline.