By WCCO-TV Staff

MINNEAPOLIS (WCCO) — Mayflies covered the sidewalks and just about everything around downtown St. Paul Thursday morning.

The Minnesota Department of Natural Resources says the short-lived insects are found in almost all freshwater systems.

Mayflies are very sensitive to chemical pollutants and decreased oxygen levels. A large hatch can be considered a good sign for the health of our environment.

The mayflies also act as food for birds and fish.

Last summer, Hastings shut off street and parking lot lights in the downtown area, as well as along the bridge and riverfront, when it came time for the mayfly hatch.

Some years, the mayfly hatches can actually be seen on radar, though WCCO director of meteorology Mike Augustyniak says that wasn’t the case with this week’s hatching.