Mystery Slick Spotted On Charles River

BOSTON -- Crews were trying to figure out the source of a chemical spill on the Charles River on Thursday.

Raw Video: Mystery Slick On Charles River

The slick, which stretched for about 300 yards, was spotted between the Longfellow Bridge and the Charles River Dam late Thursday morning.

Crews originally thought a barge on the Cambridge-side of the river leaked some kind of chemical -- possibly fuel or hydraulic fluid.

"The barge is on the Cambridge side that we think is the source of the leak. The barge on the Boston side doesn't seem to have anything leaking," said Boston Fire Lt. Michael Towns.

But a spokesman for the barge company that was working on the Longfellow Bridge, New England Bridge Contractors, said they checked their barges and they were not leaking anything into the river.

As the spill dissipated, investigators concluded that a passing vessel unknowingly leaked a few gallons of gas into the waterway.

State police asked amphibious sightseeing vehicles and other boats to stay in the center of the river as crews tried to find the source of the leak and identify the chemical.