The orca became entangled in a crayfish pot line and dragged the cray pot for several hundred yards.
Experts say the orca appeared to have teeth marks around her neck, apparently after other orcas tried to rescue her. They were unsuccessful, so Rhys Cochrane dove down to free her.
"Just before I dove down to cut the line, about five other orcas, including one massive bull, came around, and that's when I started getting a little bit scared," Cochrane said.
Cochrane says once he cut the rope, the orca was fine and swam away.
Experts say orcas are smart animals and didn't attack him because they knew he was trying to help her.