Polar bears are relatively efficient swimmers, for such large beasts. Certainly they are not comparable to salmon or pot-smoking Olympic Champions, but they are still impressive.
While in the water they paddle efficiently with their front feet, and use their back feet as rudders. They can swim at a speeds of 6.5-10 kph and paddle non-stop for 166 kilometers. The beasts have been observed swimming several kilometers from the nearest ice or land. While swimming, they do keep their eyes open and their nostrils shut. Their ears are flattened onto their heads. On the other hand, polar bears may stay underwater for up to 2 minutes. They're also capable of jumping completely out of the water 7'-8' feet, with a swimming start. They have been observed catching seals in that manner.