At least 4,500 customers of Benton PUD were without power starting about 4 p.m. Monday in central and west Kennewick.
A transmission line that feeds two substations went out, but power was restored in Kennewick by about 4:30 p.m. by rerouting power.
PUD workers continued to patrol power lines to find the source of the outage.
The outage snarled traffic.
Cars on North Edison Street were backed up at the Highway 240 on-ramp with traffic lights there not working.
At the boundary of Kennewick and south Richland, the stoplight at the busy intersection of North Steptoe Street and West Gage Boulevard lost power.
Franklin PUD reported at the same time that service was out in part of downtown Pasco and also in the area of Douglas Avenue and A Street in east Pasco.
No cause for the outage was immediately determined.
Benton PUD also had an outage for about an hour Sunday morning near Center Parkway and Gage Boulevard with 472 customers losing power.
That outage was due to a squirrel on the line.
This is a developing story and will be updated.