Maryland officials applied chemicals to three ponds Sunday to kill the notorious northern snakehead fish, voracious predators from China that threaten native fish species.

Officials say the applications of two herbicides, diquat and glyphosate, would rob fish of oxygen by killing aquatic plant life. Most fish were expected to die in the next couple of days. Any fish that survive will be killed in the next week with the fish poison rotenone.

"This is the beginning of the end for the snakehead fish," said Heather Lynch, Department of Natural Resources spokeswoman. "Time is up."

Water quality is expected to return to normal within weeks because herbicides and fish poison break down fairly quickly, Lynch said.