|Full name||Douglas Seneca Gjertsen|
|National team||United States|
|Born||July 31, 1967|
Phillipsburg, New Jersey
|Height||6 ft 5 in (1.96 m)|
|Weight||185 lb (84 kg)|
|College team||University of Texas|
Douglas Seneca Gjertsen (born July 31, 1969) is an American former competition swimmer, Olympic champion, and former world record-holder.
Gjertsen was the third member of the record-setting U.S. team in the men's 4×200-meter freestyle relay at the 1988 Summer Olympics in Seoul, South Korea. The American team of Troy Dalbey, Matt Cetlinski, Gjertsen and Matt Biondi set a new world record with a time of 7:12.51. He also received a bronze medal for swimming for the third-place U.S. team in the preliminary heats of the men's 4×100-meter freestyle relay.
Four years later at the 1992 Summer Olympics in Barcelona, Spain, he was the fourth member of the third-place U.S. team in the men's 4×200-meter freestyle relay; the American team of Joe Hudepohl, Mel Stewart, Jon Olsen and Gjertsen won the bronze medal with a time of 7:16.23. Individually, he finished eighth in the final of the men's 200-meter freestyle, recording a time of 1:50.57.
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.
Gjertsen is currently the head coach for SwimAtlanta, and has served as the personal coach for one of the best Latvian swimmers, Andrejs Duda. He currently serves as the personal coach for former American record holder Amanda Weir.
- List of Olympic medalists in swimming (men)
- List of University of Texas at Austin alumni
- List of World Aquatics Championships medalists in swimming (men)
- World record progression 4 × 200 metres freestyle relay