Deputies say Jesse Sebade was at a lake campsite for a family reunion when he decided to drink some beer and listen to music in his truck, which was parked facing the lake near an embankment.
Just before 3 a.m., one his friends turned off the truck and told Sebade to get some sleep, according to Kittitas County sheriff's deputies.
A short time later the same man heard the truck roll down the embankment and into the lake. By the time members of the camp realized what happened, deputies say the truck was already under water.
Several people tried to swim down and rescue Sebade from the truck, but it was too dark and the lake was too deep.
A Kittitas County sheriff's diver later found Sebade inside the truck, which was about 30 feet below the surface and 45 feet from shore.
The truck was in neutral and the emergency brake was not engaged, according to deputies. The truck's doors were unlocked and the window was rolled down about five inches.