Duluth firefighters doused several small fires Thursday afternoon on the former Interstate Bridge, now a fishing pier.

The cause of the fires hadn't been determined as of Thursday night and the case remained under investigation, according to Assistant Fire Chief Clint Reff.

Someone driving over the nearby Blatnik Bridge, which towers above the fishing pier, saw smoke and reported the fire at about 2:45 p.m. Thursday. The Duluth Fire Department arrived to find several fire hotspots, but ran into problems because the pier was unable to safely accommodate firefighters and their equipment, Reff said. Firefighters instead extinguished the fire on the pier and pilings from land using a ladder truck, and from the water with the help of the U.S. Coast Guard.

Damage to the pier was minimal, Reff said. The fishing pier remained open to the public as of Thursday night.

The Interstate Bridge carried trolley and railroad cars - and eventually automobiles and pedestrian traffic - between Duluth and Superior from 1897 to 1961, when it was replaced by what's now the Blatnik Bridge.

The Interstate Bridge's center span was removed in 1971; a portion of the northern part of the bridge later was converted for use as a fishing pier.