Doppler Radar Captures Massive Mayfly Emergence!
The Evening of June 23, 2012

On Saturday evening, June 23 2012, a massive mayfly emergence occurred along the Mississippi River beginning just after 9 pm. By late evening, mayflies were swarming in La Crosse, La Crescent, and points up and down the river. While the emergence of mayflies from their river bottom mud dwelling can occur at various times through the warm season, this particular event was one of the best seen on radar yet. In the radar time lapse loop from 9 pm to just after 1030 pm (below), the yellows and oranges indicate a large magnitude of airborne mayflies.

Also very evident was the northward track to the mayfly radar 'echo'. This movement was due to the south wind direction over the area at emergence time. The radar would indicate the bugs were carried north, off of the river, into Blair and Taylor Wisconsin. The radar beam over these locations are detecting mayflies at over 3000 feet above the ground! Their existence was confirmed on the ground north into Trempealeau county near Galesville.

Further south along the Mississippi River, the NWS radar in Davenport, Iowa detected the emergence as well. The mayflies were seen on radar along the river from north of Davenport to about Bellevue, Illinois. Because the beam rises above the ground as it travels further from the radar, the mayflies can only be detected closer to the radar. For example, the Davenport, Iowa radar beam is at about 5000 feet above ground by the time it reaches Dubuque. While observers did note that mayflies emerged in Dubuque Saturday evening, no radar echo was seen in the area - probably because they "flew under the radar". 

To learn more about the mayfly life cycle, go here.

Other river fly activity: July 3 2012 in La Crosse, July 28 2012 in La Crosse, the eastern Iowa Caddis fly emergence from August 11, 2012, or the Minneapolis emergence image of July 16, 2012.

Radar Loop Radar Loop


Pictures From The Following Day

Picture #1

Picture #2

From the Stoddard-Ferryville, Wisconsin area


Picture #2

Picture #6 Picture #4

Picture #2

From the Prairie du Chien, Wisconsin area


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This web page and the tracking of mayfly activity in the Upper Mississippi River is accomplished by interdisciplinary groups and agencies including the National Weather Service, the U.S. Fish and Wildlife Service, the U.S. Geological Survey, and the Wisconsin and Minnesota DNR. Volunteer observers and photographers also contribute to this work.
Contacts: Dan Baumgardt (National Weather Service), Mark Steingraeber (U.S. Fish and Wildlife Service) is the U.S. government's official web portal to all federal, state and local government web resources and services.