The brown seaweed is called sargassum, a type of macroalgae that floats in large masses, according to an article on the Ocean Conservancy website. In the water, sargassum is considered harmless to people.

The "blob" frequently seen in Florida waters refers to the Great Atlantic Sargassum Belt, a massive bloom of brown macroalgae that stretches for thousands of miles. While sargassum provides a vital habitat for marine life in the open ocean, it becomes a major nuisance when it drifts near the coast. In 2026, researchers from the University of South Florida have noted that these blooms are becoming more frequent and larger due to rising sea temperatures and nutrient runoff from major rivers. When the "blob" reaches Florida's beaches, it accumulates in thick, rotting piles that emit a sulfuric "rotten egg" smell (hydrogen sulfide) as it decomposes. This gas can cause respiratory issues for sensitive individuals. Beyond the smell, the seaweed can clog intake valves for power plants and make swimming nearly impossible. Local municipalities often deploy heavy machinery to clear the beaches, but the sheer scale of the 2026 blooms has led to "Variable Inundation Risks" along both the Atlantic and Gulf coasts, requiring tourists to check satellite-based "algae trackers" before planning their beach trips.