The Royal National Lifeboat Institution at Teddington found a man clinging from a wooden beam after his boat had capsized last Sunday.
The crew retrieved the man and handed him over to waiting police officers and an ambulance crew.
Mr Butterfield said: “The water going towards the weir goes very, very fast. It was lucky he got hold of the wooden beam because if he had been swept into the weir he would probably have been hurt and it could have been fatal.”
“He was stuck there but we managed to get to him. He was absolutely freezing.”
Mr Butterfield said the man was taken to hospital but has since been released and is not injured. He also thanked his colleagues, praising their efforts “in difficult conditions.”
A Metropolitan Police spokesman said: “Police were called at 2.55pm on Sunday, March 5 to reports of a male kayaker in difficulty in Teddington Lock.