(Monroe County, Fla.) — The Department of Health in Monroe County (DOH-Monroe) reminds residents and tourists in the Florida Keys that this is the time of year that we generally experience an influx of Sargassum that can build up at our county’s beaches.

Over the past several years, Sargassum has become more abundant in the Western Atlantic and throughout the Caribbean and is causing worldwide concern.  Historically Florida has experienced high levels of Sargassum in coastal waters and on local beaches.

Sargassum is a naturally occurring seaweed that is brown in color and floats freely on the ocean surface.  It is abundant in both the Atlantic Ocean and the Gulf of Mexico and often washes up on beaches in Florida.  As it rots, it gives off a substance called hydrogen sulfide.  Hydrogen sulfide has a very unpleasant odor, like rotten eggs.  Although the seaweed itself cannot harm your health, tiny sea creatures that live in Sargassum can cause skin rashes and blisters.

Hydrogen sulfide can irritate the eyes, nose, and throat.  If you have asthma or other respiratory illnesses, you will be more sensitive to hydrogen sulfide.  You may have trouble breathing after you inhale it.

Hydrogen sulfide is not known to cause cancer in humans.   If you are exposed to hydrogen sulfide for a long time in an enclosed space with little air flow (like some work exposures), it can affect your health.  However, hydrogen sulfide levels in an area like the beach, where large amounts of air flow can dilute levels, is not expected to harm health.

DOH-Monroe provides the following tips on how people can protect themselves and their families from exposure to Sargassum:

  • Always supervise children at the beach.
  • Avoid touching or swimming near seaweed to avoid stinging by organisms that live in it.
  • Use gloves if you must handle seaweed.
  • People should not use Sargassum in cooking because it may contain large amounts of heavy metals like arsenic and cadmium.
  • Stay away from the beach if you experience irritation or breathing problems from hydrogen sulfide – at least until symptoms go away.
  • Close windows and doors if you live near the beach.
  • Avoid or limit your time on the beach if you have asthma or other respiratory problems.
  • In the rare event you experience severe breathing difficulties, consult a healthcare provider immediately or call 911.

Sargassum season is March through October.

For more information including the NOAA Experimental Weekly Sargassum Inundation Reports, visit

This seasonal Sargassum increase is unrelated to the Red tide bloom in Sawyer Key that led to DOH-Monroe issuing a health caution on March 14, 2023.

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