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Effects of Contamination

Washing clothes in the lake.

Washing clothes in the lake.


What does “Lake Atitlán is dying” really mean?

It means that the lake’s ecosystem is being destroyed, that it is now so contaminated that the threat of ecological collapse is real, and could be imminent. The lake actually has too much life in it — too many putrefactive organisms. The water is overloaded with phosphorus and nitrogen, the nutrients that algae feed on, which causes oxygen depletion and eutrophication.

The main causes of nutrient overloading in the lake – poor wastewater management, chemical agriculture, and commercial tilapia farming — must be stopped. And in the meantime, they must be counteracted. Damage must be mitigated if the lake is to stay alive long enough for measures to stop the contamination to take effect. And unfortunately, any such measures are currently a pipe dream.

The consequence of decades of contamination is that today Lake Atitlan has under 100 meters of oxygen-rich water remaining. Below that are around 250 meters of dead water that no longer supports aquatic life. If this layer continues to rise, species will die out in greater numbers, the water quality will get even worse, and local communities will suffer the ill effects on their health and livelihoods.

Death by Eutrophication

Eutrophication is killing Lake Atitlán from the bottom up.

Eutrophication is killing Lake Atitlán from the bottom up.


That’s the fate awaiting Lake Atitlán if urgent action is not taken.

Eutrophication, or depletion of oxygen, occurs when the water is overloaded with nitrogen and phosphorus, which are food for algae, including the toxic cyanobacteria, a malodorous blue-green algae that occurs naturally in waterways and oceans worldwide. Although nitrogen and phosphorus occur naturally and are essential plant nutrients, nutrient overloading imbalances the ecosystem.

Algae can multiply quickly when there is an overabundance of nitrogen and phosphorus, and they deplete the dissolved oxygen level in the lake by breathing it. After the algae dies, sinks, and decays it is broken down by bacteria, a process which can use up all the available oxygen deeper down in the lake. As the low oxygen layer rises, the species that used to inhabit that water die off.

Nutrient overloading from agriculture runoff, human waste, and tilapia farming has created conditions for cyanobacteria to grow out of control as it feeds on nitrogen and phosphorous in the contaminated water. Cyanobacteria was first detected in Lake Atitlán in 2009, when the algal bloom was large enough to cover a significant portion of the lake surface. Various strains of cyanobacteria were also detected in subsequent years, albeit in smaller blooms, and in August 2015 a thick microcystis cyanobacteria bloom appeared.

Impact on Communities

View of Lake Atitlán from Solalá.

View of Lake Atitlán from Solalá.


Local communities’ health and livelihoods are at risk.

Hundreds of thousands of people around Lake Atitlán depend on the lake as their primary water source for agriculture, household use, and drinking. Contamination threatens their health and livelihoods as  Lake Atitlán faces both ecological and economic collapse.

An estimated 20% of the local population suffer from intestinal infections including e-coli, giardia, and amoebas. The level of e. coli in wastewater that leaves the treatment plants is frequently tens of thousands of times above the safe limit, and cyanobacteria blooms release toxins into the lake that can be deadly if ingested by humans.

Fear about the health effects of pollution has a negative impact on the tourism industry, which is important to the local economy and which has suffered particularly severely during cyanobacteria blooms. When news of cyanobacteria blooms reaches potential tourists via media reports, social media, and word-of-mouth, they are deterred from visiting, and the local economy suffers.

Fishermen now struggle to survive on what they can catch in a lake that used to support abundant life. Much of the soil in the Atitlán Basin is so contaminated from decades of chemical agriculture that it can no longer support farming without the use of yet more toxic chemicals.