The Danube is a muscular source of power and a haven for fish, birds, and amphibians. It is also the conduit for four metric tons of microplastics a day that wash into the Black Sea. Just ask Andreas Fath, "the Swimming Professor" of Germany's Furtwangen University, who swam all its 2,700 kilometers (1,678 miles) in a monumental 57-day journey to raise awareness of pollution in the Danube.
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