Police got a call about damage to a power pole and a roadside barrier near the intersection of McDonald Road and Ballam Road late Sunday night.
Police found a woman's body in the river, off the side of the road, and after a short search pulled a Ford F-150 pickup truck from the river Monday morning.
Chilliwack RCMP Const. Tracy Wolbeck said police believe the woman was driving the truck and that there was a man with her at the time the truck went into the river.
"We are doing everything possible in an effort to locate what we believe is a second victim in this tragic accident," Wolbeck said in a written statement.
"We want to be able to bring closure to the families involved in this and will continue to do whatever is necessary to recover him."
Wolbeck said the RCMP dive team will return to the river Thursday and will use sonar equipment to try and find the body of the missing man.
She said Chilliwack Search and Rescue may also be assisting the police.