PETIT-BOURG — First, a stench catches you even before you can see the shoreline. Then a tide of red algae comes, which pours onto beaches, rocks, the mangrove. Coming from the deep and carried by marine currents, this algae is known as sargassum.

"This is no longer an emergency, it is a calamity," said the Minister of Ecological Transition and Solidarity, Nicolas Hulot, on his arrival in Petit-Bourg, Guadeloupe, where a hundred protesters from the local anti-sargassum collective were waiting. He was accompanied by the Minister of Deep Seas, Annick Girardin.

Since 2011, the inhabitants of the Caribbean islands have regularly been accosted by these rafts of algae, which can reach several thousand square meters and which give off nauseating smells when decomposing. But this year, the scale and duration of these algae blooms are unprecedented. Worse still, the problem could be prolonged.

"We are facing an exceptional phenomenon not simply because of its magnitude, but one which may increasingly repeat itself due to climate change," says Mr. Hulot.

"They have been there for six months," says Jocelyne Traventhal-Hatchi, spokesperson for the anti-sargassum coalition. "Six months that we've played host to H₂S and NH₃."

H₂S and NH₃: hydrogen sulfide and ammonia, two of the toxic gases identified in the fumes. However, depending on the nature of these sargassums, other toxic components may be active, such as arsenic, which increases fear within the community.

Government mobilization was late. Too late; plunging inhabitants into a sense of abandonment. There had been "a delay in action and a lack of coordination between actors, and the state is not exempt," Ms. Girardin said.

Welcome to Sargasso Land.

At each stop the ministers were met by a reception of residential committees, mostly wearing protective masks, eager to tell the reality of their daily lives for the last few weeks and months. The daily stench that the winds are not strong enough to sweep away, nausea, vomiting, diarrhea, swollen eyes, irritated throat. Their testimonials which caused officials to close schools and transfer students away from the decomposing mounds of algae.

For the small islands of the Guadeloupe archipelago, whose economy is largely based on tourism, the consequences are even more catastrophic. Some of them, like Marie-Galante or Terre-de-Bas, were cut off for several days because the ships could not enter or leave the ports, which had been invaded by brown algae. The fishing boats are immobilized in the middle of a pestilential mud that corrodes and oxidizes everything, just as gas emissions blacken and degrade household appliances. The tourists have deserted; shops and restaurants are closing.

Clearing efforts are slow going with only a fraction of the algae having been cleared. The only town hall of Capesterre-de-Marie-Galante has already spent half a million euros. Nevertheless, even if the exchanges were sometimes fraught, this visit was welcomed as a testimony that the state, finally, cared for these territories "at the end of the world." "Welcome to Sargasso Land," Marlene Miraculeux-Bourgeois, the mayor of the town, said upon the arrival of the two ministers, recalling that, in seven years, no minister of ecology had moved to Marie-Galante. As they left citizens begged, "don't give up on us."