Just when you thought it was safe to go in the water: climate change is exacerbating aquatic microbial hazards

Aquatic microbiomes deliver critical ecosystem services, spanning primary production, nutrient cycling, degradation of contaminants and climate regulation. However, a small fraction of the microbial assemblages inhabiting marine and freshwater ecosystems can also have detrimental impacts on human populations that use these aquatic environments for recreation and food provision. Some naturally occurring aquatic microorganisms, including diverse species of pathogenic bacteria and toxic microalgae can cause a wide range of often severe human health effects. Furthermore, anthropogenic pollution leads to the introduction of allochthonous microbiological hazards, including diverse enteric viral, bacterial and protozoan pathogens present in urban runoff. Notably, the threats posed by many harmful aquatic microorganisms are increasing due to climate change. Chronic and acute increases in water temperature enhance the growth and virulence of pathogenic and toxic microbes, often triggering bloom events that can threaten human health. Furthermore, increasingly frequent intense precipitation events escalate intrusions of allochthonous pathogens within coastal pollution and runoff. These often-overlooked microbiological implications of climate change have the potential to profoundly impact the health and economies of human populations that increasingly rely on marine and freshwater ecosystems.