One side of the Casco Bay Bridge was closed to traffic for about 90 minutes Sunday evening  as crews worked to fix a malfunction in the span.

The closure only affected motorists driving to South Portland from Portland, while traffic heading into Portland was allowed to use the bridge connecting the two cities.

A bridge tender late Sunday said the southbound lanes of traffic heading from Portland into South Portland reopened around 9 p.m., about 90 minutes after it was closed. He declined to comment on what might have caused the bridge to malfunction.

Sgt. Chris Mitchell of the Portland Police Department said officers were deployed around 7:30 p.m. Sunday to redirect traffic heading into South Portland away from the bridge, which spans the Fore River.

Mitchell said he was told that the bridge was malfunctioning, but he could not provide any specifics on what the cause of the malfunction was or how long it would last.

But, according to New England 511, one side of the bridge was closed Sunday evening due to an electrical issue. New England 511 is a web-based service that collects traffic data and reports vehicle crashes, bridge closings, roadwork and unusual traffic patterns.

The bridge over the years has on several occasions turned into a headache for commuters, especially if the drawbridge gets stuck or is raised to allow ships to pass through. About 15,000 vehicles a day cross over the bridge, while fewer than two ships a day pass under it. The bridge opened 630 times in 2019 to let ships pass through.