Reinelt, a long-time member of Germany’s men’s eights crew, had won Olympic gold in London in 2012 and silver at the 2016 Olympiad in Rio de Janeiro.
He died on Sunday near St Moritz, Swiss police and rowing officials said. The cause of death was not immediately released.
“His surprise death which came far too early makes me infinitely sad,” said Siegfried Kaidel, chairman of the German Rowing Federation.
“Everyone who knew him was captivated by his friendly nature. He will be missed.”
After ending his rowing career, Reinelt had gone on to complete his medicine studies and planned to work as team physician for a German under-23 squad.
International Olympic Committee president Thomas Bach called Reinelt “one of the great athletes of German rowing and a very likable person who managed to combine competitive sports and his professional training as a doctor with great success”.