The Silver carp is big, unwieldy, and requires Joe Greendyk use both hands to measure it before tossing the fish overboard into the Illinois River.

The nearly 2-foot-long aquatic menace, which now overruns the river, has become the target of a state-run monitoring program to rein in its exploding numbers.

“They’re pretty slimy and pretty strong,” Greendyk says with his hands caked in fish slime. He’s a seasonal field researcher with the Illinois Natural History Survey. “So if you don’t grip them right, they’re pretty hard to control.”

For decades, local, state and federal officials have worried the carp could bypass Chicago and breach the Great Lakes, possibly reducing populations of native species that locals like to fish. The feared spread could wreak havoc on the world’s largest fres

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