An extraordinary lake

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Lake Atitlán in the Central Highlands of Guatemala is inside an ancient caldera that has three volcanoes on its southern rim: San Pedro, Tolimán and Atitlán. The lake surface is 125.77 sq km (48.56 sq mi), its perimeter is 101.67 km and has a water volume of 25.46 km3 (6.11 cu mi), with a maximum depth of 327.56 m and a mean depth of 203.21 m. Due to the frequent variations in lake level, these numbers vary in time. 

 

In size it is approximately 18 km long by 8 km wide (from Panajachel to Cerro de Oro, though another 8 km could be added to the bottom of the Santiago Atitlan bay). Atitlán does not have any surface drainage, it is technically an endorheic lake, that filters its waters underground in the area between San Lucas Tolimán and Cerro de Oro, feeding two rivers rather that drain into the Pacific coast. It is shaped by deep surrounding escarpments of volcanic in origin, filling an enormous caldera formed by an eruption 84,000 years ago.  

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In time, the original nations settled around the lake, the Kaqchikel on the north shore and the Tz'utujil on the south shore. On the upper and northern side of the watershed, there are some k'iche' people. Nearly 95% of the population speaks a Mayan language and most are bilingual (Spanish and a Mayan language)

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Biodiversity

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Given its latitude and elevation, lake Atitlan is in the confluence of the North American Neartic biodiversity and the  Neotropical biodiversity that reached the area with the terrestrial bridge of Panama some 13 to 15 million years ago. As a result, in the upper watershed conifers and oak stands prevail, while near the waterfront avocados, bananas and heliconia.  

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The lake and cyanobacteria

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With the demographic growth of the 20th Century, increasing amounts of wastewater reach the lake, the expansion of the agricultural frontier into lands predisposed for erosion has carried soils with a high content of phosphorus into the lake, which along with a growing volume of solid waste have enriched the previously clear and clean lake water. As a result, in 2009 the lake had the first great cyanobacteria bloom that mobilized residents around the lake.   

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The scientist and experts from San Carlos National University, the Regional Engineering School of Sanitary and Hydraulic Resources, the Landivar and Del Valle de Guatemala universities have assessed all posible solutions known to reduce or eliminate pollution from wasterwater and have concluded that in the Atitlan watershed there is: 

• Not enough land for wastewater lagoon treatment

• Not enough forest or planting fields to irrigate with treated wastewater

• The massive collection of solid waste from dry toilets is not economically, socially or practically viable

• The best wasterwater treatment plants around the world will pollute the lake water (it's not viable to completely clean wastewater) 

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Therefore, wastewater should be exported and treated outside the watershed. 

 

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How to treat water water outside the watershed

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• There is land for waterwater treatment lagoons 

• There are planting fields to irrigate with treated wastewater  

 

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To be defined with the participation of residents, authorities and stakeholders  

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• Who contribute the land for wasterwater treatment plants and lagoons

• Who receives the treated wastewater.