Douglas Seneca Gjertsen (born July 31, 1969) is an American former competition swimmer and Olympic gold medalist.
He was the third member of the United States' world record 4x200-meter freestyle relay team at the 1988 Summer Olympics in Seoul, South Korea. The 1988 relay team set the world record with a time of 7:12.51. He was also the fourth member of the United States' bronze medal 4x200-meter freestyle relay team at the 1992 Summer Olympics in Barcelona, Spain with a time of 7:16.23
He attended the University of Texas at Austin, and swam for coach Eddie Reese's Texas Longhorns swimming and diving team. He was a three-time individual NCAA champion and a nine-time relay NCAA champion. He was inducted into the Longhorn Hall of Honor in September 2006 for his accomplishments not only at Texas but also on the Olympic stage.
Doug is currently a coach for SwimAtlanta and for one of the best Latvian swimmers, Andrejs Duda.