The SUV was operated by a Long Beach Police officer and responding to a report of a surfer in distress.
The sunbather, a man in his 40s, was rushed by helicopter to Nassau University Medical Center.
He had internal injuries and broken bones, but they were non-life threatening.
Police were investigating why the police officer failed to see the sunbather.
The victim's chair was low to the ground, and it may have been obstructed by the sand.
The surfer got out of the water without injury.