Dennis Martinus Hendrikus Rijnbeek (born August 7, 1972 in Haarlem) is a former freestyle swimmer from the Netherlands, who competed for his native country at the 2000 Summer Olympics in Sydney, Australia. There he took over too early in the qualifying heats of the 4 × 100 m freestyle relay, which meant disqualification for the Dutch relay team. He retired from the sport in 2001.