The Ocean ‘Was the Color of Chocolate.’ Mexico Declares War on Seaweed.

Cmdr. Álvaro Villanueva and his crew were a half mile off Mexico’s coast last month when they spotted their target: a mustard-brown seaweed known as sargassum that had massed to gargantuan size.

The Mexican Navy had been after this patch for hours, monitoring its approach via satellite and tailing it with a drone to help establish a closer heading.

Switching on conveyor belts that extended from the stern of the ship into the water, the crew began to haul in streams of seaweed, dumping it onto the hull, where workers packed it in with a bulldozer. It was one of the best days of the Mexican Navy’s sargassum-hunting season: more than 400 tons of seaweed removed in just a few hours.

The operation amounts to the front line of Mexico’s war on sargassum, declared earlier this year as the seaweed choked off the country’s tourism industry.

“It all joins up and keeps growing,” Commander Villanueva said on another recent trip to sea. He stood on the bridge of his ship, the Natans, a one-time garbage collecting vessel that was retrofitted to suck sargassum out of the water. “We call them agglomerations when a cluster forms that’s the size of a soccer field.”

Since spring, when the sargassum bloom begins an annual period of growth, thousands of tons of the seaweed have washed up on Mexico’s Caribbean shores every day, blighting a part of the country with an economy built on its turquoise water and powdery white sand.