Alan Poindexter, a two-time space shuttle astronaut, has died after a personal watercraft accident in Pensacola, Florida, NASA said on Monday.

Poindexter, 50, was riding WaveRunners with his two sons in Little Sabine Bay at Pensacola Beach on Sunday when the accident occurred, a spokesman for the Florida Fish and Wildlife Conservation Commission told Reuters.

"Poindexter and his 22-year-old son Samuel were riding on one WaveRunner and his older son, 26-year-old Zachary, was on another", spokesman Stan Kirkland said. "They stopped and apparently Zachary did not see them stop. He struck the right rear or the right stern of their personal watercraft. His watercraft went up and apparently struck Captain Poindexter in the back. Both Captain Poindexter and Samuel were ejected."

"The former astronaut was pulled from the water and taken to the beach where friends attempted to revive him. He was flown by helicopter to Baptist Hospital where he died from his injuries", Kirkland added.

"Poindexter's sons were not injured. All three men were wearing life jackets as required by law. It's technically still under investigation until our report is completed," Kirkland said but added that investigators were satisfied it was an accident and considered it "a terrible tragedy."

Poindexter made two space flights during his career with NASA. In February 2008, he was the pilot aboard the shuttle Atlantis on a mission to deliver the European Space Agency's Columbus laboratory module to the International Space Station. Poindexter returned to space in April 2010 as commander of the shuttle Discovery on one of the final cargo runs to the station before the shuttles were retired.

""The NASA family was sad to learn of the passing of our former friend and colleague Alan Poindexter," NASA wrote in a Facebook post. ""Our thought and hearts are with his family."

In an interview Poindexter told the Rockville Gazette: "I feel privileged and honored to have flown. It's been a tremendous ride, looking back on the legacy and accomplishments, like the Hubble telescope and the launching of the International Space Station in 1998."

At the time of his death, Captain Poindexter was Dean of Students and Executive Director of Programs at the Naval Postgraduate School.