Dagmar Rehak was a West German breaststroke swimmer who participated in the 1976 Montréal Summer Games. She was eliminated in the heats of both the 100 and 200 metres. With the medley relay, she was disqualified in the heats due to a false turn. The following year, she won the bronze medal with the medley relay squad at the Jönköping European Championships. Domestically, she earned West German national titles over 100 metres in 1974, 1977 and 1980, and over 200 metres in 1974-75 and 1978. She later regularly participated in masters swimming events.