[Korra makes a face at Sigma, like one might make at an unbearable pun but she decides to forego the explanation of where Polar Bear Dogs come from.]

The waterbending tribes have been living on the south and north poles for a long time now. It's handy, when you can just built everything out of snow and ice.

[It's pretty extreme, especially compared to the other parts of the world, but other than the Earth Kingdom, no other nation is as surrounded by their element as the Water Tribes.]

We even have a huge palace, made of ice.