Lake Chichoj owes its existence to geology that is still actively reshaping the landscape. The lake basin formed where at least three dolines coalesced - depressions created when gypsum dissolved at depth, leaving the ground above unsupported. Evidence of this process is visible two kilometers south, where sulfate-bearing springs emerge along the active trace of the Chixoy-Polochic fault in the Chixoy River valley, building large travertine fans. These springs discharge far more water than their immediate upslope catchments can supply. The closest catchment capable of feeding them is Lake Chichoj's own, which sits 400 meters above the spring outlets. Water routes through the basin follow complex karstic pathways, disappearing into limestone passages before resurfacing downstream. The lake's outlet drains into a cave - a geological detail with serious implications during storms, when debris could block the cave entrance and cause the lake to rise by four meters before overflow finds an alternative path.

Despite its modest size - just one kilometer long and half a kilometer wide, with a maximum depth of 32 meters - Lake Chichoj behaves like a much larger body of water. It is strongly stratified, its upper layer turbid and poorly mineralized, sitting atop a deeper layer that is five degrees cooler and heavily mineralized. The thermocline that separates these layers holds at roughly seven meters depth. Most water circulation stays confined to the upper layer, where the average residence time is only 18 days. Once or twice a year, usually in January or February, the lake mixes completely. This overturn can happen rapidly, bringing nutrient-rich bottom water to the surface in a sudden upheaval. The catchment has been designated a Protected Area, an acknowledgment that the lake's ecological balance depends on what happens in the surrounding landscape, where deforestation and urbanization have been accelerating for decades.

The deterioration began in the 1950s. Deforestation, agricultural fertilizer runoff, and untreated city wastewater from San Cristobal Verapaz poured nutrients into the lake, triggering eutrophication - the suffocating overenrichment that turns clear water cloudy and living ecosystems into dead zones. Environmental studies that began in the 1970s identified untreated sewage as the primary culprit rather than agriculture. The most visible symptom is the water hyacinth. Enormous floating rafts of Eichhornia crassipes spread across the lake surface, blocking sunlight and consuming oxygen. Workers harvest the invasive plant continuously to keep open water accessible, composting the massive hauls into horticultural fertilizer. But the hyacinth is only the surface problem. Chromium contamination, building since the 1950s, reached 20 times natural background levels by 2005. Local witnesses report that the extensive marshlands now ringing the lake were open water within living memory, and a distinct ancient shoreline sits more than a meter above the current water level.

Lake Chichoj presents a hazard that no one has yet measured. The marshlands surrounding the lake likely sit atop sediment-filled dolines similar to those that formed the lake itself, which means the ground could resume subsiding at any time if gypsum continues dissolving at depth. No monitoring of subsidence has ever been undertaken. The next phase of collapse could be gradual or sudden - even instantaneous. Meanwhile, the lake's outlet cave poses a separate risk: if debris blocks it during a storm, the lake level could rise by four meters before finding an alternative overflow path, flooding areas that have since been filled and urbanized. Some sewage is now rerouted away from the lake through pipes across the marshlands before emptying into the Rio El Desague downstream. It is a partial measure for a lake that exists because of what is missing underground - dissolved rock, vanished water, the hollow spaces that swallow the landscape from below.