Fish Die-Off at Lake Suchitlán Highlights Deepening Environmental Crisis in El Salvador

In August 2025 residents of Copapayo woke to thousands of dead fish on the shore of Lake Suchitlán, the country’s main hydroelectric reservoir (Cerrón Grande) covering 135 sq km. By the following months, invasive water lettuce (Pistia stratiotes) carpeted nearly 70 % of the surface, plastic waste accumulated, and fish kills became frequent. The lake, a Ramsar wetland supporting 12 of El Salvador’s 14 native fish species, also supplies roughly 28 % of national hydroelectric power.

The Guardian

Biologists link the lettuce bloom to high nutrient loads from the Lempa River, which receives fertiliser runoff rich in nitrogen and sulphates. Gabriel Cerén, a biologist, explains: “What facilitates the reproduction [of the water lettuce] is the high amount of nutrients that the Lempa River gets from fertilisers that end up in the lake and concentrates a high amount of nitrogen and sulphates.” The dense mats depleted dissolved oxygen, fostering cyanobacterial growth and fish mortality. Laboratory analyses by the University of El Salvador’s toxicology lab (Labtox) conducted weeks after the die-off found nutrient levels within expected ranges and no active cyanobacterial bloom, but sampling was hampered by the surface cover. Residents reported aerial spraying of chemicals to remove the lettuce, though no authority has confirmed such actions.

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President Nayib Bukele’s administration has offered no explanation. The environment, agriculture and health ministries have not commented on the removal of water lettuce or the possible use of chemicals. Requests for water testing were routed through court-linked channels, limiting public reporting.

The Guardian

Local fishers and activists accuse the government of neglect. Alberto Castillo, a boat operator, says the lake’s collapse forced residents to join clean-up crews, cut incomes to about 30 % of previous earnings, and rely on alternative jobs. “The lake needs an urgent study,” he adds, noting repeated fish deaths and the resurgence of invasive plants. Residents also report increased mosquito populations, skin rashes from swimming, and rising gastrointestinal and respiratory infections.

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• “People are starting to come back very slowly, but during these months we had to take different jobs, getting only 30% of what we were making before.” — Alberto Castillo, Boat Operator

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• “We’ve had fish die before, but nothing like this. First the water lettuce, then the plastic, now the fish – it demands attention.” — Alberto Castillo, Boat Operator

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• “We eat them out of necessity,” Avalos says. “Our bodies have had to adapt.” — Noel Avalos, Resident

The Guardian

• “What facilitates the reproduction [of the water lettuce] is the high amount of nutrients that the Lempa River gets from fertilisers that end up in the lake and concentrates a high amount of nitrogen and sulphates,” — Gabriel Cerén, Biologist

The Guardian