Nottinghamshire Police acted quickly to rescue two men from freezing cold water at Farndon Marina in North End, Farndon.
One of the men is believed to have slipped on an icy pontoon before falling into the water at around 1am on Saturday.
The second man is thought to have got into difficulty after trying to help him.
A nearby resident heard cries for help and called 999 before police were quickly on the scene and found the men.
Officers managed to pull one of them clear and got hold of the other man, but initially struggled to get him out of the water as he was unconscious.
The determined officers eventually helped him out of the freezing water but he remained unresponsive and is believed to have been suffering from hypothermia.
He was taken to hospital by ambulance and remains in a stable condition.
Nottinghamshire Police Chief Inspector Chris Sullivan said: "Thankfully the swift response by these police officers and brave actions to pull them free may have saved both of their lives.
"Police officers always put the safety of the public first and are always there when people are in their hour of need.
"With support from our ambulance service colleagues, these two men were given the help they needed and I hope they both make a full recovery from this traumatic incident."
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