Flatwater canoeist Joachim Mattern was a member of the East German K-4 1,000 at the 1972 München Olympics, which was eliminated in the semi-finals. The crew experienced a surprise elimination by finishing fourth behind Romania, an unheralded Finnish crew, and Hungary. He also came in sixth in the K-1 1,000. Four years later Mattern returned to the Olympics at Montréal and claimed a gold and a silver medal with his partner Bernd Olbricht in the K-2 500 and the K-2 1,000. In 1977 both repeated the medals at the World Championships. Mattern also claimed a silver medal at the 1970 Worlds with the K-4 1,000 and two bronze in the K-2 1,000 in 1970 and 1973.
Domestically, Mattern won the K-1 1,000 nationals in 1969 and 1972, and the K-2 1,000 titles in 1970, 1972-73 and 1978. With the K-4 of TSC Berlin he added national titles in 1969 and 1970. Mattern later started a coaching career first in the former GDR and after reunification he became German chief coach for the flatwater kayak canoeists until 2005 and was engaged again in 2009.