Ryan Arens said he was delivering packages just before Christmas when he heard a dog "screaming and crying and going crazy."
The employee told the Great Falls Tribune in an article published Friday that he quickly delivered a package, then drove to the other side of the pond, where he saw the animal.
"I could see the dog trapped about 10-15 feet off of shore, with ice all around it," Arens said.
An older man was on a boat trying to rescue the dog, according to Arens, but was having difficulty chipping away at the ice to get closer — so the UPS employee knew what he had to do.
"I stripped to my boxers and got the guy out of the boat. Then, I slid the boat out onto the ice, using it to distribute my weight," Arens said. "I shimmed out to where the ice was thin."
Soon, he crashed through the thin ice and fell from the boat. Arens said he noticed the dog "was starting to go under," and so he swam for her. Arens was able to grab the dog's collar and tried to pull her to thicker ice.
Arens told the news outlet the two were able to slide across the ice and back to shore together, where a bystander gave him a blanket. They went into the older man's home where they warmed up before authorities arrived to help.
"Animals are my weakness. It was the highlight of my 14-year UPS career," Arens said.
He told the Tribune that he found where the dog's owner lived, and happened to have a delivery for him. He spotted the rescued dog — named Sadie — in a car, and said "she was freaking out" when she saw him.
"She must have remembered me," Arens said. "It sure made me feel good."