A diesel fuel spill appears to have caused a car accident that prompted closure Wednesday afternoon of a stretch of Highway 20 on Whidbey Island.

Trooper Chris Merwin with the Washington State Patrol said diesel fuel was spilled along a two-mile stretch of the highway.

The spill caused slippery road conditions along the sharp curves of Highway 20 near San de Fuca. That’s where a Toyota Corolla traveling south on Highway 20 slid and struck a Pontiac Aztek near the intersection with Arnold Road.

“The gentleman came across the centerline,” said Nicole Betz, who was driving behind the Aztec and witnessed the accident. “It looked like he was going to stop in time but he didn’t.” She noticed that both drivers had slowed before colliding.

Firefighters detoured traffic at Holbrook Road and Sidney Street while the crash was cleared and a crew from the Washington State Department of Transportation sanded the highway to improve road conditions.

Merwin said the crash is still under investigation. Investigators don’t know how the diesel fuel was spilled on the Highway and nobody reported any instance of following a leaking vehicle.

Merwin didn’t know yet whether any citations will be issued.