Streams and rivers form conspicuous networks and life therein figures among the most diverse on Earth. The common wisdom has been that biodiversity in these fluvial networks accumulates downstream similar to water and sediments. Combing sequencing with ecology, Katharina Besemer, Gabriel Singer and Tom J. Battin have now shown together with colleagues from Switzerland and the United Kingdom that this does not hold for microorganisms, which show their highest diversity in headwaters.

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