They were so tiny, I hadn't even noticed they were alive the first time I scooped; I doubt that my camera would pick them up. The critters are about the size of this period. At first, I thought it was dust that had sifted through the screen I had put over the pond to keep out pine needles that could get through the net, but the screen has been off for over a week, and there are more patches, so this time I looked more closely. The "dust" seems to be the husks of eggs/cocoons, and there were tiny white squiggly things as well as the "flea" things. I'll see if I can get a picture of the patches. Too bad I scooped them all out this morning!
Edit: I tried to find them online; Daphnia (water flea) came up, but I don't think that's what they are...they seem too solid and black, compared to pictures of nearly transparent water fleas.