For more than 100 years, beachgoers in Lynn and Nahant called it “the smell.” It came from a rare algae that settled and decomposed on local beaches. For decades, scientists were puzzled about how to eliminate the odor. Finally, in 2008, the Department of Conservation and Recreation decided to send out work crews with front-end loaders to scoop up the algae every morning from April to November.
That plan worked for five years. But last July, the odor returned for about six weeks when the brown algae, known as Pilayella littoralis , was allowed to cake up on Nahant and Lynn beach. As it decomposed in sand under the hot sun, the algae, which can rise up like a bronze carpet on hundreds of yards of sand, released a sulfide odor akin to the smell of rotten eggs.