A sound like trumpeting elephants is the best way to keep the dreaded Asian carp out of Lake Michigan, a British expert said Wednesday.

"It's similar to putting your hand in hot water and pulling it out," he said. "It causes them to turn tail and go in the opposite direction."

Sound at 160 to 170 decibels, about the same level that irritates humans, will repel the invasive fish but is only one-tenth of the level that would stun them. A Saturn rocket generates 150 decibels; rifle fire, 130 decibels. The barrier will generate a pulsing rather than steady sound.

"We had to answer the question of what's unpleasant to a fish," Nedwell said. "It sounds rather like an elephant trumpeting, or maybe a mad bagpiper."