Is it safe to swim with sargassum?

The short answer

For most people, swimming with some sargassum floating around does not usually cause serious problems. But there are times when it is better not to, and the final word always belongs to the lifeguards, the beach flags and the notices from health authorities. This guide is not medical advice.

What can happen in the water

• Itchy or irritated skin. Tiny animals live among the seaweed, such as larvae and hydroids, and some people get itching or small bumps from them. It usually fades soon, but if you have a strong reaction, see a health professional.
• Getting tangled or not seeing well. Large mats are awkward to swim through, hide what is underneath and can make it harder for lifeguards to see you. If there is a lot, stay out.
• Murkier water. When there is a lot of sargassum near the shore, the water usually looks darker.

What happens on the sand

The bigger issue is usually not the fresh sargassum in the water but the piles that build up on the sand and rot. That sargassum smells bad and gives off gases that can bother some people. We cover it in the guide Sargassum smell and health.

When it is better not to swim

• When lifeguards or the flags advise against it.
• When Florida or county health authorities have issued a notice for that beach.
• When sargassum forms a continuous layer along the shore or in the water.
• When you have sensitive skin or open cuts, or have reacted to it before.

Practical tips

• Swim where the water is clearest and away from the mats.
• Rinse off with fresh water when you get out.
• Keep an eye on children: they love playing with seaweed, which can hide small creatures.
• Do not let your dog eat sargassum from the sand.

How we help

Our index tells you how much sargassum there is, not whether the water is safe for swimming: that is for the authorities to decide. What we can do is help you pick a beach with less sargassum today. If yours says "Heavy sargassum", look at the nearby beaches before you leave home.