The Japanese Akita acted when the middle-aged man jumped into the ice-cold Methil Docks in Fife, Scotland, according to Deadline News.
Reaching his owner in the water, the canine stayed by the man's side until they were rescued by firefighters.
A source said: "We don't really know the circumstances surrounding this, but we believe it was an attempted suicide [and] it looks like the dog tried to stop it."
A local Fire and Rescue Service spokeswoman stated: "We were called to a water rescue at the docks in Methil at 5.09am.
"A middle-aged man and a Japanese Akita were rescued from the water. The male was in the water first and the dog jumped in after him."
The dog was handed over to the owner's family, while the owner himself was taken to hospital for treatment.
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