Zooplankton—tiny aquatic animals known to graze on bacteria—are ineffective at removing fecal microorganisms from sewage-contaminated water, according to a new study. The findings challenged the assumptions of the researchers that these tiny animals could act as natural cleaners by inactivating harmful pathogens in freshwater and saltwater environments. The hypothesis was that zooplankton would consume or neutralize fecal microorganisms, potentially reducing the risk to human health after water contamination. But the results told a different story.

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