http://www.newsweek.com/florida-seaweed-blob-sargassum-health-effects-1798097

The gargantuan clump of seaweed that has been slowly floating toward Florida is now washing up on beaches across the state and might be harmful to people and wildlife nearby.

The blob of seaweed is about 5,000 miles across, and is composed of sargassum seaweed, which naturally blooms in the Sargasso Sea but can spread widely across the Atlantic, forming the "Great Atlantic Sargassum Belt."