Today I came across a pond in the Netherlands where I noticed a cloud, for lack of a better word, of small red creatures swirling around near the surface of the water, as can be seen in this video:
And here is a picture:
The surface was unfortunately quite reflective, but the motion is visible. The creatures were too small for me to see any structure to them with the naked eye. Some tadpoles can be seen in the video, which are much larger. They would swim straight through the cloud now and then, so perhaps the tadpoles consider the red stuff food. The entire cloud consisted of various dense clusters connected with less dense or thinner parts, as can be seen to some extent in the video, and its total size was perhaps 2 meters or so.
What was I looking at?