An oily spill or runoff of unknown size shimmered along the Virginia side of the Potomac River on Thursday as at least six government agencies scrambled to determine its source, size and composition.

The sheen, which the U.S. Park Police said extended from Gravelly Point, just north of Reagan National Airport, to Jones Point, just north of the Woodrow Wilson Bridge, could be seen in part from the ground, but the Park Police and U.S. Coast Guard launched helicopters to survey the extent and source of the contamination.

Coast Guard Petty Officer David Marin said personnel on those flights identified the oil as coming from an outfall at Roaches Run, a tidal pond that leads directly into the Potomac just north of the airport and between the George Washington Memorial Parkway and a railroad line.

Booms were placed to capture the oil and stop its spread, Marin said. Ten soiled Canada geese were captured and taken in by a bird-rescue organization for cleaning.

“We’re not prepared to name any responsible party because there are so many variables,” said Julia Robey Christian of the District’s Department of Energy and Environment, as she stood near the containment booms that had been placed in the small-boat launch inlet at Gravelly Point. “There is not any elevated reason for concern as to public health, if this is mineral oil, because that’s nontoxic. The concentration of what’s in the river is also dissipated.”

Authorities had not determined the composition of the contaminant or named it, but Christian and others said it could be runoff from streets and parking lots. Although some officials pointed to Dominion Power, which had a 13,000-gallon spill at its Crystal City substation Jan. 24, Dominion spokesman Rob Richardson said there is no evidence that the oil in the river involved the utility. Richardson said Dominion is cooperating with all the agencies looking into it.

The river was a turbid brown Thursday, full of mud and in some cases tree branches washed downriver by rain and snowmelt.

The District of Columbia owns the riverbed, but the Virginia shoreline is overseen by the Park Service, the Metropolitan Washington Airports Authority, Arlington County and the city of Alexandria. The Coast Guard took control of the scene and tapped into a federal oil-spill-liability trust fund to pay for the services of contractors and responders, at least until a source of the oil has been determined.

Each agency heard reports of the spill or runoff at different times in the past few days. Christian said her department has been hearing reports about oil spills for several days in various spots in the river. The Potomac Riverkeeper Network began alerting supporters to the oil Wednesday afternoon, and Virginia state Del. Mark Levine (D-Alexandria), who heard about the contamination from a constituent, began calling agencies Wednesday night, he said in a Facebook posting.