A massive seaweed bloom in the Atlantic Ocean is drifting towards the Florida coastline and health experts are concerned it may cause respiratory problems for beachgoers in Florida and the Gulf of Mexico.

According to CNN, the bloom of sargassum is currently twice the width of the continental United States (approximately 5,000 miles) and may be the largest ever recorded.

Sargassum can become a hazard to marine life but health experts warn the risk to humans occurs when the seaweed hits the beaches. The seaweed accumulates, rots, and emits dangerous toxins and is more than just a nuisance. They say the gas emitted from the rotting algae is hydrogen sulfide, which can cause respiratory problems.

According to the Florida Department of Health, hydrogen sulfide is an irritant to the eyes, nose, and throat. “If you have asthma or other breathing illnesses, you will be more sensitive to hydrogen sulfide. You may have trouble breathing after you inhale it,” the agency says on its website.

The department cautions that odors from most substances in outdoor air are not at levels that can harm your health, but workers who are collecting and transporting Sargassum should wear protective clothing, such as gloves, boots, and gas filter half masks.

The department also warned that seaweed contains arsenic, making it dangerous if ingested or used for fertilizer.

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