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Mayfly Invasion Leaves Behind Massive Mess

MINNEAPOLIS (WCCO) -- A yearly summer tradition many people don't look forward to is underway this week.

Millions of mayflies are emerging from the Mississippi River.

National Weather Service radar from two days ago shows the scope of the swarm, with the aquatic insects emerging from the Mississippi River near La Crosse, Wisconsin.

The bugs only live for about a day, but the staff of the Mississippi Lock and Dam #3 near Red Wing see firsthand how they leave a mess for the ages.

(credit: CBS)

Lockmaster Tim Tabery's crew cleaned up some 30 massive mounds of mayflies over the last couple of days.

"The lights turn on, they love the white light, and here they come," Tabery said. "All the piles were underneath the lights, and next day is clean up time."

Tabery and his crew know to expect mayflies will emerge from the river annually to lay eggs and die within a day.

"They're wet and they're heavy," Tabery said. "I'm guessing thousands of pounds."

Tabery and his crew hatched their own cleanup plan, using pitchforks and a hose.

"Two guys were working for six hours yesterday," Tabery said. "They feel it in their backs."

Once the mayflies land back in the water, they leave behind a stinky scent for days that reminds Tabery of dead fish.

Dealing with the yearly disturbance has become part of the job for Tabery and his staff.

"The fish are happy, but the staff here at Lock 3, no," Tabery said. "It's a lot of work to clean up."

Mayflies do play a big role in the ecosystem by providing food for fish and birds.

Scientists say a large emergence of mayflies is actually a sign of a healthy body of water.


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