The trio from Letterkenny Garda station were on their way from Dungloe Court in an official Garda van on Tuesday at 11.30am when they noticed a woman in Dungloe lake.
Two of the officers, Garda Paul McGee and Darren Carter who are both in their 20s, waded into the icy waters in full Garda clothing and rescued the woman from the lake.
Their colleague, Garda Sean Mulroe, then helped the pair to take the woman ashore.
The woman, who is in her 50s, was taken to Letterkenny General Hospital where she received treatment.
Eye-witness Benito Colangelo, who lives overlooking the lake, said the Gardai deserve medals for bravery.
“When it approached the lake I could see the van turning and went to the lake. Three of the Garda got out of the van and two jumped straight into the lake.
“I was on the phone and I immediately put the phone down and ran outside to see if I could help. There was a lady in the water which they pulled out and saved her life.
“All praise to the two Gardai that jumped it. They were in full Garda gear, didn’t have time to take anything off and it was ice cold.
“They put the woman’s safety ahead of their own and they certainly deserve praise for it,” he said.
A Garda source confirmed an incident took place at Dungloe Lake but said the three Gardai involved wanted to play down the incident.
“It was a miracle that the three lads just happened to be driving past at the time. They certainly saved her life but they want to play the incident down,” he said.