Mayfly Watch campaign


Another year of Mayfly Watch has come to an end. Mayfly Watch is an effort to track the seasonal activity of mayflies along the Upper Mississippi River - when they emerge in swarms that can number in the millions, and also when they are not present. 

This year, we had observations of emergences at two different sites, one in Minnesota and one in Wisconsin. Observers reported heavy emergences on July 7th and July 16th. We also had 412 "negative" observation records, where observers reported they looked for but did not see mayfly adults, subadults, and other activity. Thank you all for your efforts! 

Another way to track mayfly activity is by looking at weather radar. According to the National Weather Service, only light to moderate emergences occurred this year between June 1st and August 3rd (

The gif below shows radar from Davenport, IA on July 1st, 2023.

Mayflies are an important food source for fish and other wildlife. They need clean, oxygenated water, which makes them an indicator for water quality. Unfortunately, mayfly swarms are becoming smaller in recent years. As this article from The Washington Post explains, mayflies face many threats including pollution and climate change.

Your observations of mayfly emergence are critical in helping scientists understand how mayfly emergences are changing We hope that you will join us again next year to record your observations of mayflies (present or absent!) along the Upper Mississippi River.  

Learn more about Mayfly Watch


Erin Posthumus


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