A locomotive derailed on a railroad bridge spanning the Mississippi River in St. Paul early Wednesday, spilling some 3,200 gallons of diesel fuel into the water.

Absorbent booms to collect the spilled diesel were placed shortly after it was reported just south of the St. Paul Downtown Airport, according to Walker Smith, a spokesman with the Minnesota Pollution Control Agency.

The derailment occurred around 2 a.m. on the Hoffman Swing Bridge between St. Paul and South St. Paul when one of the two Union Pacific Railroad locomotives jumped the tracks, Smith said.

“When that happened it punctured one of the (locomotive) fuel tanks,” he said.

The locomotives were moving a tank car from one St. Paul rail yard to another. The tank car also slipped the tracks, but Union Pacific workers put it back on the rails and moved it from the bridge.

Union Pacific workers put four pieces of absorbent boom into the river, the farthest of which was eight miles downriver.

“We have not seen any evidence of diesel beyond that point,” said Kristen South, Union Pacific’s director of media relations. She added that the company also had boats in the river vacuuming the diesel from the surface.

“There is no timeline yet for completion of cleanup,” South said.

Smith said there’s been no sign yet indicating an impact on wildlife. The diesel floats on the water surface and shouldn’t be a significant threat to fish, Smith said.

Boaters may want to avoid the area because of the absorbent booms placed in the area, he said.

The cleanup is being monitored by the MPCA and the U.S. Environmental Protection Agency.

The swing bridge was closed, as was river barge traffic around the low-slung span.

The derailed locomotive was being placed back on the tracks Wednesday evening. The bridge was expected to undergo a final inspection before being reopened Thursday morning, allowing normal river traffic to resume.

The cause of the derailment remained under investigation Wednesday evening, South said.

No one was injured in the incident.