This video says about itself:
ANYONE WHO TOOK A PEEK IN A CLEAR DITCH HAS SEEN THEM: the little red spiders that swim in the beautiful contrasting green of the water plants. They seem to roam about aimlessly, like simple red little balls with sprawling legs. Yet there are smaller species, not coloured red, but inconspicuous green or pale yellow. And you have to be an attentive observer to distinguish these minuscule dots in a jar full of jumping water fleas, where they move in more or less steady tracks, like planets between sparkling stars.
Worldwide there are over 5000 water mite species, with large differences in shape and habits. Some species are very similar to species on land.
Translated from the Dutch EIS entomologists:
Feb 8, 2016 – Water mites are tiny, spider-like aquatic creatures. In the Netherlands, this group is well studied because they are used as indicators of water quality. It is therefore noteworthy that in recent years as many as nine new species of water mites have been found in the Netherlands. This brings the total number of species for our country to 267. …
In a recent article in Nederlandse Faunistische Mededelingen No. 45 eight new species were reported. Since the publication of this article again a new species for the Dutch fauna has been found, by Cynthia Kruijff-Van der Voorn of Waterschap Scheldestromen: Arrenurus denticulatus. This species is internationally very rare and had only been found in France, Romania and Sweden.