A mix of dense fog and fire smoke, referred to as “superfog,” engulfed a stretch of Interstate 55, roughly 30 miles northwest of Monday morning, causing a massive pileup that killed at least seven people and injured over 25 others.

It’s unclear which collision sparked the string of collisions that included 25 different crashes in the northbound and southbound lanes at three different points along the highway. Aerial footage showed a highway blocked by destruction. Fog combined with smoke nearby from marsh fires severely reduced road visibility and caused drivers to , including three tractor-trailers. Two trucks ended up catching fire, . At least one vehicle was sent over the railing of the Manachac Swamp Bridge into the water below.

Because of the low visibility, are asking people involved in the crashes to identify themselves to account for everyone. First responders are combing through each crashed vehicle to ensure they are unoccupied. The impact portion of I-55 remains close and won’t reopen until a damage assessment is completed. Lance Scott, a driver involved,

“I’ve never seen a crash like this. I mean I’ve traveled south Louisiana for quite some time and I’ve seen fog, but the pocket of fog we saw coming over the Manchac Bridge... It was like something you’d see in the Central Valley of California. It was total fog. Couldn’t see in front of you.”

If you’re ever caught in a similar situation, be sure to do everything in your power to stay safe. First, turn on your headlights. It will slightly improve your visibility while making you more identifiable to other drivers. Second, reduce speed. Giving yourself more time to react in unpredictable conditions is vital. Driving in low visibility is no joke.