By Sabri Ben-Achour
Snakehead fish are an invasive species from China, first found in the Potomac River in 2004. The fish turn up regularly now and scientists know their numbers are increasing, but their impact remains unknown.
In the shallow water of a tidal pool at Mason Neck State Park in Virginia, fisherman Kirk Comer spots a fish THAT IS 2 feet long with tiger-like stripes hiding among the weeds.
"Monster! Look over there's four of them together, I see five, I see four, there's the fifth one back there, oh yeah!"
They're looking at Snakehead fish.
"The Snakeheads have taken over this small pond," he says. "I was just trying to fish some to see if I could get 'em out of the water for [the park service]. No luck yet."
Park Rangers say the fish arrived in the pond just a few weeks ago when the Potomac River flooded. It's not clear what impact they've had on the other creatures that live, or used to live, in the pond -- or for that matter in the rest of the Potomac watershed.
"No evidence that they're decimating any other fish populations, but the fact of the matter is we probably wouldn't be able to see that anyway--in previous studies of introduced fishes it takes a decade or more to really see the effects on populations of fish," says Paul Angermeier a scientist with the U.S. Geological Survey.
Angermeir says the biggest fear is that the Snakehead might out-compete native Largemouth bass. Even as scientists look for signs of that, the Snakehead's population and range are growing. They've been found in 80 miles of the Potomac from Great Falls on south to Colonial Beach, and in every tributary in between.