HARRIS COUNTY, Texas -

Investigators are trying to figure out what caused a driver to crash his car into a bayou in northeast Harris County.

Harris County deputies told Local 2, a passerby noticed a black Ford Mustang in the water off Greens Road near Air Center Saturday.

Deputies believe the driver was headed west on Greens Road and, for some reason, left the road.

They said the car hit a guardrail, went airborne, over a culvert and landed upside down in the water.

A man, the only person in the car, was killed. He hasn't been identified.

The Harris County Sheriff's Office is investigating.