Three weeks after oil coated and killed several birds on the south Washington and north Oregon coasts, officials say they still don’t know where the sticky petroleum product came from.

But they say they’ve done their best to clean up the areas that were affected by the mysterious balls of tar that washed up — and they’ve ended a unified command effort that brought together multiple Washington, Oregon and federal agencies to investigate.

Samples of the sticky substance were seen as far north as Long Beach all the way down to Yaquina Head, Oregon. They were first reported on May 19, when tar balls were spotted near Beards Hollow near Ilwaco and confirmed by different state agencies.

At least 10 birds had been found covered in oil by May 21, and three of them later died. All the affected birds found were common murres.

Since then, more than 100 people from a dozen federal and state agencies — including the U.S. Coast Guard, Oregon Department of Environmental Quality (DEQ) and Washington Department of Ecology — were involved in the response to the environmental incident, collecting nearly a ton of oily debris and cleaning 36 miles of beach.

Statistics:

Total oily debris collected: Nearly 2,000 pounds (almost a ton) across Oregon and Washington

Total beach miles surveyed and cleaned: More than 300 miles surveyed and 36 miles cleaned in Oregon and Washington

Total responders: 113 individuals from 14 agencies/companies

Responders recently took advantage of the low tides following stormy weather along the coast to resurvey and clean the impacted areas, according to DEQ.

The agency added that, while the unified effort is over, the investigation continues.

As the tar is mostly cleaned up, the state agencies ask if anyone does find oiled birds or other wildlife, they should avoid contact with the animals and call 1-800-22-BIRDS (1-800-222-4737). People should not touch any tar balls when they see them on the beach, and should report them to the National Response Center at 1-800-424-8802.