The Oklahoma Highway Patrol says a 76-year-old woman was killed Sunday in a crash on SH 18 south of Agra in Lincoln County.

Laura Ann Knopfel, 76, of Covington, was pronounced dead at the scene by Chandler EMS, the OHP reports.

Knopfel was driving a 2009 Chevrolet Silverado pickup southbound on SH 18. The patrol says for unknowns reasons, the vehicle departed the roadway to the left and traveled down a ditch into a shallow water creek before striking the creek bed. The accident occurred about 12:40 p.m. Sunday.

Cause of the accident is listed as unknown. Troopers said seat belts were equipped and in use.

Troopers were assisted at the scene by Lincoln County Sheriff's Deputies, Chandler Police Department, Agra Fire Department and Chandler Fire and EMS.