I went to St. Louis Botanical Gardens yesterday with my friend Joan. Here are a couple pictures of a Great Blue Heron I took just for you, Addy! He flew across the pond/lake the koi were in, and I'm sure he feeds regularly there, but there are no worries he will eat the adult koi in that pond! They weigh far more than the bird.
And, just for giggles (I know this is a bird post, but to follow the story ...) here are a couple of pics of the koi. The smallest in this pic is still close to 3'.
There were also grass carp that were larger. One was well over 3'. I had no idea grass carp had no whiskers, and their face is totally different than koi. Eyes very wide set, on the edge of the face, and much smaller mouth, kind of round rather than oval. Slick body, too, look more scaleless than koi. In this pic, the grass carp is on the left, koi on the right.