The source of last week’s fuel spill into the Potomac River remains unclear, U.S. Coast Guard Commander Michael Keane said Monday.

Authorities have been able to determine that the spill contained fuel oil. The afternoon briefing was held at Gravelly Point, a park and boat launch just north of Reagan National; the spill likely began near the Arlington airport.

“The sheening from Gravelly Point has ceased, but you will see some tidal action that will create some rainbow sheens still in the area,” Keane said.  

As time goes on, the oil is becoming harder and harder to track. “It has been significantly degraded because of weathering,” Keane said. “Right now I have not ruled out any sources.” Additional samples have been collected for further testing, with results expected Wednesday. Authorities initially believed the spill may be related to last month’s blizzard, but have since ruled out any significant link.

At the briefing, Danene Birtell, interim manager of Oil Programs for Tri-State Bird Rescue & Research in Newark, Del., said “approximately 30 [affected] animals have been captured: 29 Canada geese and one mallard duck.”

The animals that Tri-State takes in are given full veterinary exams and washed at the group’s facilities in Delaware, Birtell said; if they are healthy, the birds will be released back to their natural habitats over time with aid from the Coast Guard and other authorities.

One goose has died because of exposure to oil, Birtell said. The organization is continuing to assess the situation and look for affected wildlife.

According to Keane, because of absorption of the oil in the water and air over the past few days, there is a chance the source of the spill will never be found. For now, he said, the main goal of the Coast Guard “is to ensure we minimize impact to the environment.”

“It’s extremely difficult to try and judge how much has been out there,” he said. “One tablespoon of oil can cover an entire football field, so in our estimation this is not a very significant spill. It’s rather minor.”

Photo by Tri-State Bird Rescue & Research, Inc