LA CROSSE, Wis. (WKBT) -

We had our first big Mayfly hatch of the season Sunday night.

The video shown above was shot in downtown La Crosse.

The hatch was so large you could see it on radar maps. The bugs are harmless and they're actually a sign of a healthy river because they can only reproduce in areas with high-quality water.

"These mayflies will feed the fish that are in the water column and are eating a lot of detritus and organic matter that sinks in river and so they are definitely a big part of the food web of these systems," said Gretchen Gerrish, assistant professor in UW-La Crosse's biology department.

Gerrish said this isn't the last time the Mayflies will hatch this summer,  but whether or not it will be as big as Sunday night is still up in the air.

NWS: Upper Mississippi River Valley Mayfly Tracking

Mayflies on wall

Mayflies

Mayflies on the ground

Mayflies on light

Mayflies on heron

Mayflies cover an ATM

How would you like to get some cash from this ATM? Thanks to Ryan Hollis for sending this picture from La Crescent.

Mayflies cover the gas pumps in at this Trempealeau gas station

Mayfly hatch in Trempealeau from Saturday night. Thanks to Kelly for the picture.

Mayfly hatch as seen from Trempealeau on Saturday night from Joshua Hanson

Mayfly hatch as seen from Trempealeau on Saturday night from Joshua Hanson.

Possible Mayfly hatch showing up on radar

The Mayfly hatch was so large it could be seen on radar.