This specimen appears to be of the same species as this one collected in the same spot two months earlier. The identification of both is tentative. This one suffered some physical damage before being photographed, too, so the colors aren't totally natural. I was mostly photographing it to test out some new camera setting idea, which worked really well for a couple of closeups.
These are pretty much always called Water Pennies.
These interesting insects are not mentioned in trout fishing literature, but they turn up once in a while in my Eastern samples and I understand they are also common in the Midwest.