Back in 2002, an unnamed labrador-alsatian cross fell into the River Tees in Middlesbrough. The dog got into difficulties, and seemed likely to be about to drown. Passers-by were horrified, and seemed unable to help.
But then a seal appeared, and helped the dog to the shore. The seal, and two of its friends, then watched the dog on the shore until the fire brigade arrived to look after him. "It was just like the dog had a guardian angel", reported eye witness Chris Hinds.
More on this story, including a stock image of a seal: Seal saves drowning dog