Over the weekend, a large diesel spill developed on the Columbia River near downtown Wenatchee, Washington. So far, state officials haven’t been able to locate the source of the spill.

People started to notice the spill on Friday. At that time, it reached a mile long and some 30 feet wide on the Columbia. The spill smells strongly of diesel, but the Washington Department of Ecology is testing a sample of the spill in a lab to be sure.

The agency was able to deploy a boom on Sunday, after Saturday’s high winds died down. But they’re still sleuthing for the source as more diesel-like substance continues to pool on the Columbia.

The river is very full and choppy, which has made recovery of the spill more difficult.

Ecology spokesperson Camille St. Onge said now they’re deploying a torpedo-shaped sonar device to explore the murky waters.

“So we can try to locate an object or source of something along the shoreline and then get a diver down there to plug it up if we do find an old pipe,” she said.

St. Onge said Ecology has already checked all Wenatchee’s mapped pipes, but this spill might be coming from an old abandoned pipe.