BOSTON -- One side of Boston’s classic “Salt and Pepper” bridge has been closed to pedestrians after an inspection late Thursday night discovered a support beam in need of immediate repair.

The Department of Conservation and Recreation closed the sidewalk on the west side of the Longfellow Bridge until further notice.

The department also announced that the bridge will be closed to spectators who normally line the bridge on the Fourth of July to see the city’s fireworks.

“We recognize this is an enormously popular local, and even national event, but our top priority is ensuring public safety,” said DCR Commissioner Richard K. Sullivan Jr.

The inspection found a serious deterioration of a steel support structure under the sidewalk.

Pedestrians will be detoured to the opposite sidewalk, which remains open.

The state has spent more than $5.5 million on repairs to the bridge since August 2007. Full repairs are not expected to be completed until the fall.