Great picture, Seamus. I tried downloading the picture and bringing it into CS5 for closer examination and from the look of the pixels on my screen I'd guess it's a pretty extreme crop. But it looks to me as if the problem, if it is a problem, is from shadows cast on the pond and the pond's concrete edges. The interference isn't just at the left edge. It's there in the center and also, to very small extent, on the right. At first glance it looks as if there's an artifact that merges into the bird on the far left, but if you look closer you realize the shadow in the background just happens to fit with the bird's coloring. What does a look at the original in color show?