An oil leak last week created a miles-long sheen along the Columbia River east and west of the Cannery Pier Hotel.

The source is believed to be a 4,200-gallon, 20-foot oil tank underneath the pier where the hotel is located, according to the Coast Guard. It is unknown how much oil has been discharged.

“We don’t have a 100 percent certainty that that is the source, but it’s highly likely,” Petty Officer 1st Class Levi Read said.

The pier formerly housed the Union Fisherman Cooperative. High tides last week likely caused the sheen to spread at least 5 miles.

The Coast Guard, state Department of Environmental Quality and Washington Department of Ecology are developing plans to access the tank, which will likely involve deconstructing part of the pier, Read said. It is unknown when the cleanup will be completed, though a containment boom has been placed around the affected areas.

“We don’t have a timeline,” Read said. “We’re working on plans to do it safely.”

Reports of the sheen began Thursday afternoon, but weather conditions did not allow for safe cleanup and investigatory operations, according to a Coast Guard news release. The first report of a small sheen came from an onlooker near the hotel, and reports originating from the Port of Astoria and Hammond came in Friday morning.

The sheen extends east of the hotel to the West Mooring Basin. Cleanup near the Hammond Mooring Basin has been completed.

Anyone with information about the potential source can email Coast Guard Lt. Cmdr. Andrew Madjeska at Andrew.P.Madjeska@uscg.mil.