Pristine beaches in Mexico and Belize are covered in carpets of foul-smelling seaweed

Millions of tons of brown seaweed is washing up along Mexico's beaches and it’s putting the country’s post-COVID travel boom at risk.

Sargassum seaweed has been washing up on the Caribbean coast in record amounts. It gives a brown tint to crystal clear waters and emits a sewage-like stench when it washes ashore, according to the University of South Florida.

There were 24.2 million tons recorded in the last month in the Caribbean region, up from 18.8 million tons in May.

The boom in sargassum poses a "significant threat" to the country's post-pandemic tourism recovery, analysts from bank BBVA warn. Particularly in Quintana Roo state, home to destinations like Cancun, Tulum and Playa del Carmen.

Mexico's Navy and local workers have been drafted in to remove it from the water and sand.

"The sargassum is not a problem that can be solved, but must constantly be addressed, mainly in the summer months," BBVA said on Monday.

Mexico's GDP from tourism took a 25 per cent hit in real terms in 2020 due to the pandemic, even though the country never closed its borders. In 2021, however, the sector rebounded to near pre-pandemic levels - but the upward trajectory is in danger unless the seaweed is controlled.

Researchers blame multiple factors, including climate change, human sewage, agricultural runoff (water leaking out from fields) and dust blowing west from Africa's Sahara Desert.

Since 2011, seaweed in Mexico and across the Caribbean has exploded for reasons scientists do not yet fully understand.

Belize has recently seen an uptick in sargassum seaweed polluting its beaches too. The locations where high concentrations are particularly bad are Hopkins and Placencia in the south of the country.

We spoke to Laura McMullen, a sustainability