WRIGHTSVILLE, Pa. (AP) — A bridge has been closed for a second straight night because of swarms of mayflies so thick they caused accidents, authorities said.

Wrightsville fire officials said the Route 462 bridge over the Susquehanna River between Columbia and Wrightsville closed at about 10 p.m. Sunday.

Chief Chad Livelsberger said a vehicle slowing because of the cloud of insects led to a crash, though he didn't believe anyone was seriously hurt. The bridge reopened overnight.

The bridge was also shut down Saturday night after three motorcycle crashes attributed to the flies. Livelsberger says the department was dispatched to deal with one crash and saw two more crashes while on the scene. All three victims were treated at the scene.

"It was just crazy," Livelsberger told the York Dispatch on Sunday afternoon. "It was an inch to 2 inches of mayflies on the road."

Mayflies are attracted by light and congregate on roads, bridges and other surfaces. When cars hit them, the females' eggs release liquid that makes roads slick.

Livelsberger said motorists driving through a mayfly swarm should treat it like an actual blizzard, expecting zero visibility and remains creating a slick coating on the ground.

"If they're going through something like that, err on the side of caution," he said.

Lt. Sean Montgomery of the Columbia Borough Fire Department compared driving on the bug-covered surface to driving on ice or snow — but he said the winter scenario doesn't include the horrendous smell, "like dead fish."

Tom Smith of the Penn State Extension in York County said despite the hazards and annoyance that the swarms are causing, it's actually a good thing in the broad scheme of things.

"They're indicators of clearer water," Smith said. "It's indicating that the Susquehanna River's getting cleaner."