It's a rite of summer that usually seems to happen around this time of year-- the annual mayfly hatch along the Mississippi River.

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Mayflies typically hatch in mid-summer in large swarms along area rivers and lakes. And sometimes, the swarm is so large that it literally overwhelms area roads and bridges. Places like Hastings here in Minnesota and La Crosse over in Wisconsin have sometimes had to bust out the snow plows to clear off all the bugs.

And, some years, the swarm is so large that it even appears on various weather radar scans. Which may have been the case Wednesday night. KTTC-TV's Matt Benz noted on his Facebook and Twitter page that he could see the Mississippi River "lighting up on radar" due to the mayfly hatch.

The Minnesota DNR website explains why it's actually a good thing that these sometimes massive mayfly hatches occur-- it shows that the river ecosystem is healthy. The site remembers a time in the 70's and 80's where the Mississippi was so polluted (with raw sewage, mainly) that mayflies completely disappeared. Yuck.

So while this year's hatch this year doesn't seem quite as large or invasive as in a few years ago (when places like La Crosse and Dubuque had to bring out the plows to clean things up), it's still quite the site.

And while I'm glad the mighty Mississippi is healthy enough for mayflies to hatch again, I'm glad our Zumbro River here in Rochester doesn't have to contend with them!