Police spokeswoman Valeska Jakubowski says the man from Texas had jumped into the Spree river early yesterday with a 21-year-old friend.
The older man managed to swim the short distance across the river but the Texan failed to reach the shore.
Two passers-by, including a Danish lifeguard, tried unsuccessfully to save the man. He was recovered by firefighters but later died in hospital.
Jakubowski said today that the deceased man is believed to have consumed alcohol and drugs before jumping into the river. She declined to identify the man, citing German privacy rules.