Alexander Vogel, 38, said he was walking along the Landwehr canal in Berlin during the early hours Sunday when he heard a cry for help, The Local.de reported Tuesday.
"It was such a wretched noise," Vogel told the Tagesspiegel newspaper.
Vogel said he followed the noise and discovered a man struggling in the waters of the canal, about about 5 feet below the bank.
"He was pretty far from the bank, and kept sinking under the surface," Vogel said. "He managed to get back [to the side] but could not get up onto the bank on his own."
Vogel said he took off his lengthy scarf, which had been knitted by his mother-in-law, and threw one end to the man. He said two bystanders helped him remain steady while the man used the scarf to climb to safety.
Emergency responders said the rescued man, a 22-year-old U.S. citizen, was taken to a hospital and treated for hypothermia.