Around 11:15 a.m. Tuesday, Southridge High staff were notified of a possible gun on campus.
According to the Kennewick Police Department, school security and the School Resource Officer identified the student and quickly isolated him.
The student, a 16-year-old male, was in possession of a gun.
He was taken into custody at the Benton-Franklin County Juvenile Justice Center on suspicion of unlawful possession of a firearm.
Kennewick Police say there was no apparent threat to students or staff and there was no critical incident.
Due to circumstances and timing, the school was not locked down.