DISCOVERY BAY -- An elderly couple died Monday morning when their SUV veered off Highway 4 and into a drainage canal, according to the California Highway Patrol.

The crash happened about 9:55 a.m. just west of Victoria Island, Officer Peter Van Eckhardt said. The cause was not immediately known.

Witnesses driving behind the couple saw the car leave the road and stopped to help, Van Eckhardt said. One of the witnesses tried to help the couple out of the submerged vehicle, but was unable to reach them as the car quickly filled with water.

The Placerville-area couple, whose names have not yet been released, died at the scene. The cause of the accident is under investigation.

Contact Rick Hurd in Antioch at 925-779-7166. Contact Erin Ivie at 925-847-2122.