Turtles kind of come and go in my goldfish and mosquito fish pond, they usually go back to the creek, but so far no snappers. Only carolina or red eared sliders. They like to eat my purple water lilies. I object. But I don't worry too much about the ponds they are in.
Unwanted koi here - my first place is a public pond, I ask and get permission. If I get desperate they go on Craig's list. but I have a tank I can put them in and strap them in with aeration and 110 gallons of water, and then they are easy to catch when I know where they are going. I have 43 koi in the biggest pond with the biggest filter right now. Hope to get it down to about 20 before winter. We cleaned it this summer. I had like 40 of the smaller koi in the 110 gallon tank getting fed every couple of days, and a partial water change, for a week. I donated my biggest and most beautiful koi as they had outgrown the pond. Many came in too large. I pick up orphans and take them home.
While this is not a pretty pond, it is prettier now that the lilies are in it and plants fill the filter tray. Should get some cherokee purple tomatoes off it later this year. and the bees are using it to get water to take back to their hive. New photo later.
This pond is a compromise between the city and I, as a large in ground pond on a lot without a house, constitutes a secondary structure on a lot without a primary structure and would require an application for a code exemption and a lot of money. I get ready to move that whole pond will go on my trailer in about 6 hours