Just before 1:30 p.m., officers responded to a domestic violence call at a home in the 9000 block of 7th Avenue NW.
When they arrived, they found a 17-year-old girl with a slashing wound on her forehead.
Police believe the girl and her 21-year-old sister were in a heated argument that devolved into violence. They believe the elder sister grabbed a steak knife and slashed the teenager's face.
The victim was taken to a local hospital to be treated for her non life-threatening wounds.
The older sister was arrested and booked into King County jail on suspicion of felony domestic violence assault.