Tourists are seen on a beach covered with seaweed in Cancun, Mexico June 24, 2019. — REUTERS/JORGE DELGADO

MEXICO CITY — Millions of tons of stinky brown seaweed washing up along Mexico’s beaches threaten a post-COVID tourism rebound as international tourists plan summer travel, according to Spanish bank BBVA.

Sargassum seaweed, which gives a brown tint to the crystal-clear waters of the Caribbean coast and emits a sewage-like stench when it washes ashore, reached an all-time monthly high in June, according to the University of South Florida. There were 24.2 million tons recorded in the 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, particularly in Quintana Roo state, home to oceanfront destinations like Cancun, Tulum and Playa del Carmen, analysts from bank BBVA said in a research note.

The seaweed outburst defied massive daily efforts by Mexico’s Navy and local workers who scrambled 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% hit in real terms in 2020 due to the pandemic, even though the country never closed its borders. In 2021, however, the sector rebounded nearly to pre-pandemic levels, according to BBVA, which warned the upward trajectory was in danger unless the seaweed is controlled.

“The tourism sector must continue to promote new attractions so that the beaches are less and less the reason that attracts tourists to Quintana Roo.”

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

Researchers blame multiple factors, including climate change, human sewage, agricultural runoff and dust blowing west from Africa’s Sahara Desert. — Reuters