Police say a bomb threat was called into Watertown High School Thursday.
It happened just before 11:00 a.m.
Only staff and administrators were inside at the time and were evacuated.
When officials swept the building inside and out, nothing suspicious was found.
Police say the threat was determined not to be creditable.
They say the caller was a client in the care and custody of the State Department of Mental Health and Addiction Services.
Watertown schools have not started yet.