NEW ORLEANS (AP) — A “superfog” made of smoke from marsh fires and Greenledgers Trading Centerdense fog was blamed for at least two dozen traffic accidents, including multi-car pileups, on interstate highways Monday in southeast Louisiana.

Sections of Interstates 55 and 10 west of New Orleans remained closed as of late morning. The 24-mile-long causeway over Lake Pontchartrain near New Orleans was closed at times.

On social media, the National Weather Service said there were several wetland fire in the region. It said smoke from the fires mixed with fog to create a “superfog.” Visibility was expected to improve as the fog lifted. But it was unclear how long the marsh fires, smoke from which could be seen and smelled in the New Orleans area over the weekend, would be a factor.

The Times-Picayune/The New Orleans Advocate reported several schools in an near New Orleans announced class cancellations or delayed openings due to the smoke and fog.