Here's what Wisconsin looks like covered in millions of flies

This year's mayfly hatch in the Mississippi River reached Biblical proportions.

The mayfly emergence is an annual event in which mayflies leave the Mississippi River after one or two years of incubation. The flies live for up to 36 hours before they return to the water, lay a new crop of eggs, and die.

The La Crosse, Wisconsin branch of the National Weather Service (NWS) reports that the mayflies caused a three-vehicle car crash as they descended over the town. The flies caused a bow echo on the NWS radar, which normally occurs during heavy rains, and proceeded to make a Wisconsin road slick, causing a driver to lose control of her car. Two people were injured in the crash, and one was treated at a local hospital.

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Wisconsin residents captured some stunning — read: horrifying — images of the mayfly emergence, which happened on Sunday night. Check out the swarm below. --Meghan DeMaria