The biologists could pick out the snakehead at a glance: It has a torpedo-shaped body and snakelike diamonds on its side.
A long black wire connects the power source to three hand-held probes - which the scientists walking in front wave back and forth in the water. As if by magic, hundreds of fish appear in front of them, belly up.
The people in the water wore rubber waders, which insulated them from the shock. But, as the water got deeper, the biologists kept yelling: "Keep your elbows out of the water!"
As the line of scientists passed, they left a wake of hundreds of small, stunned fish in their path. It would take the fish about 20 to 30 seconds to "wake up" and disappear again into the dark water.
Once out of the water, the fish look harmless enough. They are speckled and deep green and - despite their reputation - even pretty.
The snakeheads in the cooler were to be weighed and measured so biologists could get a rough idea of the age of the overall population.
Their inner ears will be removed because they contain growth rings. The snakehead creates a new ring every day, so by counting them scientists can determine the day the fish hatched, said Scott Herrmann, a Virginia biologist.
Also, their stomachs will be sliced open so biologists can see what and how much they've been eating. Thus far, Odenkirk said, they favor inch-long killifish. But snakeheads seem to eat a lot - Odenkirk found four killifish in the belly of an 8-inch snakehead.
Some fish will be studied for their tolerance to saltwater. Preliminary results from that study showed a snakehead died in water with salt levels of 10 parts per thousand, said Mike Mangold, a biologist with U.S. Fish and Wildlife.
That's good news for the Chesapeake Bay, he said. The salinity level at a data buoy at the mouth of the Patuxent River was 13.8 parts per thousand yesterday, according to the Chesapeake Bay Observing System Web site.
After an hour-and-a-half of wading through the creek yesterday, the scientists stopped for lunch.
The fish were counted, and one was put on the grass. Despite its reputation as a "walking fish," the snakehead just flipped and flopped on the ground - the way one would expect a fish out of water to behave.
Most biologists spread out on the grass and ate sandwiches, but Odenkirk had a different meal.
He showed off a plastic baggie containing bits of fried, breaded snakehead - his own special recipe.
"Try some," he offered. "It tastes almost like a pork chop."
For previous stories about snakeheads in Maryland, go to baltimoresun.com/snakeheads.