Authorities believe Thursday's oil spill in New Bedford harbor began north of the New Bedford-Fairhaven bridge, but that's all they know about the spill's origin.

The fuel spill was discovered around 7:30am Thursday. The Coast Guard and Fire Department responded quickly, placing booms and absorbent pads in the water.

Coast Guard Lt. Derek Giffen saysofficials boarded at least 40 vessels searching for the origin of the spill, but found nothing incriminating.

Frank Corp. of New Bedford was hired to clean up the spill. Officials estimate there were 100-200 gallons of diesel fuel in the water.