Welcome...If you really want to learn more about koi ponds you have come to a great place...Lots of information and knowledge can be found here....I live in Wagoner - Its just about 45 minutes East of Tulsa....Herons once they find your pond will not stop comin' round till every fish is gone....If you don't find something to discourage him then he will consider your pond just another fish Cafe on his route....Hope you find the answer soon....if all else fails....You could try the 3 S's of ponding----Shoot, Shovel, and Shut up
.......Of course I'm not telling you thats the best way to deal with the problem-since it is illegal to shoot them
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Lawanna