Hundreds of thousands of dead fish have washed up on the shores of Lake Cajititlán in Jalisco in the past ten days.
Lake Cajititlán is about 9 kilometers (5.6 miles) long and 2 km wide. It is mid-way between the city of Guadalajara and Lake Chapala, Mexico’s largest natural lake. Fortunately, Lake Cajititlán does not have an outlet, so water and fish from the lake can not enter other nearby streams or lakes.
According to government officials, about 3 million dead popoche chub (Algansea popoche) with a combined weight of 82 metric tons were removed from Lake Cajititlán in the latest ecocide.
Initial reports contained conflicting versions of events, with local fishermen claiming far higher losses than government officials. The currently accepted figure of 82 metric tons suggests that the fishermen’s estimate was far closer to reality than the early “official” figures.
Local authorities at first tried to persuade residents that the die-off was part of a “natural cycle”. However, this idea was quickly dispelled by state and federal agencies who are continuing investigations to establish the precise causes of the ecocide. Their preliminary technical studies have confirmed that the die-off of fish was due to contaminated water with dissolved oxygen levels well below the limits for a healthy fish population. The contamination appears to originate from raw sewage entering the lake and the inefficient operation of the existing sewage treatment plants.
Low oxygen levels could also result from seasonal rainy season runoff washing excess fertilizers into the lake, increasing the water’s nitrogen and phosphorus loads, promoting eutrophication.
State authorities have issued an environmental emergency alert for the lake, but have consistently maintained that the event has not endangered the health of local residents.
This is the fourth fish kill affecting Lake Cajititlán in 2014. This latest ecocide is only one of several ecological disasters that have befallen Mexico in recent weeks.