Sligh said he acted quickly to rescue his wife, who was unresponsive after the collapse.
"Popped my shoulder back in so I could unbuckle everything so I could get over to her. Unbuckled her and pulled her into my side, which had less water," he said.
Helicopter footage from KOMO-TV showed several rescue boats in the river with several ambulances waiting on the shore.
"When you're sitting down in the water and there's all that mangled metal and bridge and you're looking around kind of pinching yourself and realizing you're lucky to be alive ... it's a pretty amazing day to tell you the truth," Sligh said.
ABC News' Rebecca Lee, Ben Gittleson, Michael S. James, Leezel Tanglao and David Kerley contributed to this story.