"Danger, Viktor, danger!"
Those are some pretty good looking koi, too. Clearly you're feeding them right and they're very happy in your pond.
I've got a pond in my backyard, too, but nothing inside even close to the size of those guys. We used to have one koi, when my kids were younger, they named "Helper" because if a ball or other floating object found it's way into the pond, he'd push it to the side for easy retrieval. Alas, poor Helper (and many of his pond mates) met his maker at the tip of a heron's beak. I caught the feathery bastard out by the pond one day and lit his ass up with a paintball gun. He never came back, but it was too late for the fish. My pond is occupied by far smaller specimens now.