Fishermen have been removing thousands of dead fish from a lake near the western Mexican city of Guadalajara.
Local media reported at least 40 tonnes of popoche chub freshwater fish had washed up on the shores of Lake Cajititlan, in Jalisco state.
One local official described their deaths as a “natural, cyclical phenomenon” that occurred every year.
However, other state and local officials have blamed poor lake management for the deaths of the fish.
The authorities are investigating whether a wastewater treatment plant is to blame for failing to filter out untreated material and thus reducing the amount of oxygen in the water.
Last year local fishermen recovered about 200 tonnes of dead fish from Lake Cajititlan. More than 100 fishermen are involved in this year’s operation.
But a local official, Ismael del Toro, said the deaths of the popoche chub fish happened every year during the rainy season.
“It is a natural, cyclical phenomenon. It happens every year and other species are not affected,” he insisted.
Another local official, Erik Tapia, suggested that the deaths of the popoche chub fish might be due to overpopulation.
“They do not have any natural predator and they are not suitable for human consumption,” he said.