Assistant Fire Chief Craig Leroy said it was not a major environmental hazard, and it appeared to be runoff from a spill on the Congress Street Bridge.
"Whatever gets in the gutter on the Congress Street bridge strains off through the scuppers,'' he said.
Peter Van Keuren, a spokesman for the state Department of Transportation, said there was a reported spill on the bridge at around 10 a.m.
"There was oil on the bridge. There were no vehicles, and we were not aware of any accident,'' he said. "We put sand down on the spill. Since then, we understand some of the material has gone into the water.''
City firefighters, with the help of the Albany County Sheriff's Department, lowered booms into the water to pick up some of the oil that was causing a sheen on the river.
Battalion Chief Robert Schlesinger said the spill trailed along for three-quarters of a mile starting near the Congress Street Bridge and winding down by Hutton Street. The heaviest concentration was by State Street.