Watch where you step this summer. A seething tangle of floating trouble is massing for a potential assault on Florida beaches. University of South Florida scientists said January was the second consecutive month that the amount of seaweed doubled, reaching 8.7 million tons, which is enough to fill about 3,000 Olympic size pools. Sargassum is a lifeline for fish nurseries, hungry migratory birds and sea turtle hatchlings seeking shelter in its buoyant saltwater blooms. But in mass quantities, it chokes life from canals, clogs boat propellers, and is a killjoy at the beach, piling up several feet deep like a rotting bog emitting hydrogen sulfide as it decomposes. “This is very rare in history,” said USF oceanography professor Chuanmin Hu, about the rapid growth. 📸 Malcolm Denemark, Meghan McCarthy/USA TODAY Network