Several people appear to have escaped injury after their Toyota Camry drove off Highway 240 and rolled through the fence into Columbia Park.
The crash happened shortly before 5:30 p.m. Saturday.
Washington State Patrol troopers and Kennewick paramedics are at the scene.
Details about what led to the rollover, including whether another vehicle was involved, are unknown at this time.
A witness to the aftermath said the flipped car held at least a woman, man and toddler.
The wreck happened near the park entrance. Traffic initially was reduced to one lane, and was backed up as cars slowly passed the scene.