While photographing something else at one of the wildlife guzzlers, I saw movement on the water surface of a holding tank...tiny gray shapes moving on or just under the water surface, converging on "something" along with an even smaller shiny black oval insect. The leaf edge showing in the image is a water iris leaf. To me, these little guys look about the same shape as a giant water bug, but they're tiny, gray and not leaf-brown, and I don't have the eyesight to detect much visually--getting them into the computer and larger helped show that they were actually alive and had legs. I'm guessing they're the nymphs of some aquatic bug, but I have no idea what. As they formed a "raft" of individuals around the brown/orange something, I'm guessing they were feeding on it--I was able to just see movement away from the iris leaf-edge out to the group.