Sargassum is a collection of seaweed and other plant material washed onto shore, often an island, by the ocean currents. At high tide, it is typically covered with seawater. At low tide, the water recedes, leaving the plant matter to bake and ferment in the sun, providing a good breeding ground for small insects and bacteria. Due to the high levels of bacteria and heat, the sargassum often smells very foul and is quite mushy, making it unpleasant to step in.

The Florida Keys and its smaller islands are well known for their high levels of sargassum covering their shores.

A sargasm bath is when an individual rolls around in the muck. This is usually done due to a dare or a loss of a bet.