Every summer since 2007, residents of coastal Chinese city Qingdao have been greeted by a mysterious “algae bloom.” No one can fully explain where it comes from. But in 2013, the New York Times reported a theory that nearby farms of porphyra (the nori in our sushi), were attracting the algae, which was then swept out to sea to blossom into a mushy green carpet.
Though it’s a delightful bright green, the annual algae inundation poses some threats. It’s harmful not only to marine life but also to humans, yielding toxic hydrogen sulfide gas once it begins to decompose. And cleaning it up before it rots isn’t cheap; in 2008, Qingdao spent more than $30 million removing it. So far, that hasn’t kept local beachgoers from diving in.