The video clip has gone viral on the internet.
It was recorded by a boat passenger near Kiak Kai pier in Bangkok. The man, carrying a lifebuoy tried to swim out to the woman, who was struggling to keep her head above water.
However, the current was too strong and he was unable to reach her. So he threw the lifebelt toward her.
The woman was saved by the lifebuoy, but he then appeared to lose out against the waves and the current, and started drowning.
The woman, who remained alert, quickly swam to him with the lifebelt, and he was able to cling to it. Both of them were saved.
According to passengers on a speedboat who witnessed the incident, the woman did not fall into the river but jumped off the pier. Some thought that she was trying to commit suicide.
The man who rescued the woman was one of the passengers on the speedboat.
After the video was posted on YouTube and other social media websites, netizens heaped praise on the woman's rescuer.
According to a Facebook user, the "courageous" man is Phitsanu Hongkamsang, a Thai Airways International engineer working at Suvarnabhumi airport.
"The man's actions are admirable. Watching this clip reminds me that not all Thais are selfish. There are many good people here," a YouTube user said.
Other internet users said the man is a hero and has their greatest respect.
However, some criticised other boat passengers who did nothing, just sat on the vessel and watched events unfold.
One netizen warned people that swimming in a pool is not like swimming in a river. As could be seen in the video, the waves and current were strong and the man only just made it back to safety.
Netizens also commented on the rescued woman.
One of them posted, "Life is valuable and please don't destroy it (if the suicide rumour's true)."
Read the original story here.