The source of an oil sheen in the Columbia River may have been identified.

The sheen was first spotted Thursday afternoon near the Cannery Pier Hotel in Astoria. It soon spread some five miles along the river.

The Coast Guard reported Saturday that contracted salvager Global Diving and Salvage had located a 20-foot-long tank underneath a pier near the boutique hotel.

The maximum potential spillage could be 4,200 gallons, the Coast Guard said. It's unknown how much oil has leaked so far.

Another aerial photo of the oil sheen in the Columbia River.

The Cannery Pier Hotel sits on the renovated dock that was once the site of the Union Fisherman Cooperative Packing Company. The cooperative, formed in 1878 by about 200 gillnet fishermen, grew out of increasingly contentious disputes between cannery owners and fishermen at a time when Astoria was one of the country's foremost fishing capitals.

The Cannery Pier Hotel, which opened in 2005, is on the end of the old "Union Fish" dock, 600 feet into the river's mouth.

The Coast Guard and others involved in the clean-up operation are figuring out the best way for workers to safely reach the tank, the Coast Guard reported.

A containment boom has been put in place on the river to limit the spread of oil, and cleanup operations are ongoing.

-- Douglas Perry