There's a relatively short list of mammals that can out swim a black lab, and killer whales are definitely on it. Check out this crazy video of a pod of orcas cruising around in shallow water in Mathesons Bay, New Zealand.
Here's what the video's uploader had to say: _"The free diver was on his way back in when he must have seen the orcas and quickly got out onto the rocks. It seemed like there was at least four orcas around him of which one was a mother with her calf.
The one orca came very close to shore where the Labrador was busy retrieving sticks from the water. He saw the whale and quickly turned around and swam back to shore with the Orca following as far as he could go."_