I live in Eastern Washington. First batch of KOI when we moved them to the new pond were taken by a heron I suspect. I bought a fake owl and have never had a problem since, and that's been 6 years or so. I also had algae problems, to the point you couldn't see the KOI, I was ready to get rid of them, 40+, when I saw one jump, swore it was a salmon. So I finally decided to purchase a UV Clarifier, after installing the next day the pond was crystal clear. My pond is 3 feet deep roughly 18ft x 20ft with not much plant coverage and takes direct sunlight most of the day. KOI jumping out of water could be signs of sickness.