A mass hatching of lake flies on a Wisconsin lake was so dense it was picked up by a local TV station's weather radar.

The radar image shared by WLUK-TV shows a large green mass over Lake Winnebago that analysts said was a swarm of millions of lake flies hatching.

Lake flies live only a few days and their larvae serve as a food source for Lake Winnebago's sturgeon, the station said.

Local witnesses posted photos to social media showing gigantic swarms of lake flies after they flew out over land.