Why Do Millions of Fish Keep Dying in Mexico’s Lake Cajititlán?
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Why Do Millions of Fish Keep Dying in Mexico’s Lake Cajititlán?

Great swathes of the surface of Mexico’s Lake Cajititlán were obscured last week as hundreds of thousands of dead fish surfaced and drifted toward the shore.

Fishy goings on

Over 100 local fishermen and conservation workers have removed almost 50 tons of freshwater fish from the lake in the western state of Jalisco in the last 10 days, after Cajititlán was struck by the latest in a string of mysterious mass deaths.

The putrid smell of rotting fish hung over the lake where workers have been busily scooping the fish from the surface, then wheeling them away, prior to shovelling them into the mouths of diggers more commonly used in construction work.

More than four million fish weighing 156 tons were hauled from the same lake last September in the worst such incidence to date. In total, 290 tons of dead fish surfaced in the lake throughout all of 2014.


The state government has compensated local fishermen. Photo by Duncan Tucker

Officials squabble over blame

PROFEPA, Mexico’s federal agency for the protection of the environment, has recommended that local officials revise the “fundamentally inadequate” wastewater treatment plants around the lake to ensure that sewage has not been flowing into the water.

However, the local government led by the liberal Citizen’s Movement has attributed the deaths to annual “natural cycles” caused by seasonal changes in temperature, while pointing out that only one species of inedible fish has been affected.

Meanwhile, state officials from the rival Institutional Revolutionary Party (PRI) have sought to blame the local authorities for poor management of the lake.


Millions more dead fish surfaced at the lake throughout 2014. Photo by Duncan Tucker

University investigation

Biologists from the nearby University of Guadalajara have described the mass deaths as “an environmental crisis.”

Investigators from the university announced the results of a study on Monday which indicates that the series of mass deaths were caused by shortages of oxygen in the lake.

The shortages were likely caused by a combination of organic matter, industrial waste and other pollutants seeping into the river that feeds the lake, the investigators said.

This could also include pesticides from nearby fields being washed into the lake by rainwater, which would explain why the deaths have always coincided with Mexico’s rainy season in the summer months.

The university investigators presented a 13-point plan to prevent further deaths and called on the municipal, state and federal authorities to take urgent action to reduce the levels of pollution in the lake.

The biologists also determined that the dead fish were in fact a species known as mojarra de lama (a type of bream) — not popoche chub, as has been widely reported.


The authorities have squabbled over what caused the deaths. Photo by Duncan Tucker

Government compensates fishermen

The local fishermen who have been helping with the cleanup operation have not been directly affected by the mass deaths because the mojarra de lama fish are inedible and other species appear not to have been harmed.

However, lakeside restaurants have suffered from the bad publicity and the Cajititlán Fishermen’s Association has reported a significant general decline in the population of all kinds of fish species in recent years.

For these reasons, the Jalisco state government has provided the 192 fishermen who make up Cajititlán’s four local fishing collectives with 18.4 million pesos (just over $1 million) in compensation over the last two years.

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