For thousands of years, the glaciers that crown the Cordillera Blanca mountain range in Peru have sustained life in countless downstream settlements, expanding with ice in the winter and releasing meltwater in the dry season. Venerated as gods by Andean peoples before the Spanish conquest, the towering blocks of ice today make up the world’s largest collection of tropical glaciers and are a massive source of freshwater in western South America. But as global temperatures have risen, the Cordillera Blanca’s glaciers have shrunk by nearly half in the past six decades, and towns from the highlands to the coast now receive diminishing flows of freshwater from glacier-fed rivers.
As the region braces for an eventual glacier-less future, concerns about the quality of water that remains are also growing. Researchers arefinding that the thawing of ice is souring water supplies in highland regions in different parts of the world, including the Cordillera Blanca. That’s because when ice retreats for good, it can expose sulfide-rich rocks that had been long hidden from the elements, producing acidic meltwater laden with heavy metals that trickles into lakes and streams. The process, known in scientific jargon as “acid rock drainage,” can render water undrinkable, corrode infrastructure, and cause confusion about the source of contamination.
In the Cordillera Blanca, which overlaps with a geological formation embedded with pyrite, an iron sulfide, government scientists have detected acid rock drainage caused by deglaciation in five gorges so far, and academic researchers have found 60 lakes to be highly acidic, including three of the four lakes that feed rivers flowing into the city of Huaraz, the region’s capital. With water growing increasingly scarce in the dry season, the local utility company plans to build a new treatment plant capable of processing the oxidized water, which is estimated to cost $10 million and take several years to complete.
However, highland villages that have long relied on glacier-fed streams have a hard time adapting. Many of them tap natural springs for drinking water but out of need continue to use water affected by acid rock drainage for farming and livestock. In time, scientists say, that acid rock drainage might also affect groundwater.
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Meltwater pools on the slopes of the Pastoruri peak in the Cordillera Blanca mountain range. Pastoruri, once a popular tourist destination, has lost so much of its ice mass that it no longer meets the definition of a glacier. The retreat of the glacier has triggered acid rock drainage, turning its meltwater a rusty-reddish color. Image by Marco Garro. Peru. Dionisia Moreno, 70, a Quechua farmer from the village of Jancu in the Cordillera Blanca mountain range, cleans sheep tripe with water from Shallap Lake. Moreno remembers when the water from the lake and downstream rivers carried trout and ran crystal clear. But as the glacier above it has shrunk away, acid rock drainage has taken hold. Moreno and other villagers stopped drinking the water several years ago, tapping a natural spring instead. But, due to need, they continue to use it for farming. “It’s not good for plants,” says Moreno. “When we irrigate with this water, the plants don’t develop fully.” Image by Marco Garro. Peru. Emilio Mendez, 46, sits on the banks of the Quilcay River near a bend where his village, Paquishca, used to keep a small fish farm. The project was abandoned as the river, which draws on glacial meltwater but is affected by acid rock drainage, became too acidic to keep the fish alive. Paquishca gets its drinking water from a natural spring that Mendez says is running dry. Image by Marco Garro. Peru. Meltwater streams into Lake Shallap in the Cordillera Blanca mountain range. The retreat of the Shallap glacier has exposed a large swath of the Chicama Formation, a geological layer that formed millions of years ago and is embedded with pyrite, an iron sulfide. Because of acid rock drainage, the water in Shallap Lake now has a pH level of less than 4 and authorities have found it contains lead, manganese, iron, and zinc at levels that exceed environmental quality standards. Image by Marco Garro. Peru. Alice Leyva tends to her animals on the banks of the Rio Negro, or the Black River, in the town of Canrey Chico in the Cordillera Blanca. Leyva grew up drinking the river’s water and washing clothes with it. But acid rock drainage from deglaciation at the river’s headwaters has limited its water’s utility. “The water has turned the rocks red and now we can’t even use it to wash clothes because it will stain them,” says Leyva. Image by Marco Garro. Peru. A villager in the town of Canrey Chico in the Cordillera Blanca holds fallen leaves covered in a rust-colored sediment on the banks of the Rio Negro, or Black River, which has been impacted by acid rock drainage. The town’s farmers use the river’s water to irrigate crops, but they say the water leaves a layer of sediment in the soil and corrodes their hoses and sprinklers. Image by Marco Garro. Peru. Water from acid rock drainage soaks the wetlands beneath the peak of Pastoruri in the Cordillera Blanca mountain range. Andean wetlands, known in South America as bofedales, have long acted as natural water filters, thanks to bacteria that help neutralize pH levels and plants like distichia muscoides, a spongy green cushion plant that absorbs heavy metals. Image by Marco Garro. Peru. Joel Salvador visits the grave of his father, Vicente Salvador, in Canrey Chico. Vicente led his community’s efforts to build a bioremediation project to treat acidic water from the Black River. He died of gastric cancer in 2021 shortly after a pilot project was installed. Joel says his father’s main source of drinking water was the river. “He drank that water almost his whole life,” says Joel. “The water used to be clean. It didn’t have such a strong flavor. Now it tastes sour, like it has lime juice in it.” Image by Marco Garro. Peru. A woman walks down a road in Canrey Chico, a town in the Cordillera Blanca mountain range. The river that runs through the town, the Black River, carries water that has been effected by climate-induced acid rock drainage. Image by Marco Garro. Peru. A shepherd herds his flock on a road near Jancu, an Indigenous village in the Cordillera Blanca mountain range. Villagers in Jancu and other communities downstream of Lake Shallap can no longer drink water from the lake or local streams because of its acidity and the presence of heavy metals. Image by Marco Garro. Peru. Residents of the city of Huaraz wash wool in Quilcay River, one of several glacier-fed streams in the Cordillera Blanca that flow with oxidized waters due to acid rock drainage. Image by Marco Garro. Peru. A resident of Huaraz washes wool in the Quilcay River, one of several glacier-fed streams in the Cordillera Blanca that flow with oxidized waters due to acid rock drainage. Image by Marco Garro. Peru. Jara Cruz, the mayor of Canrey Chico, rests by a tributary of the Black River, whose waters have been affected by acid rock drainage. Cruz jokes that the river, named after the black stones that line its banks, should be renamed “the river of rust.” “It’s useless,” she says. Since taking office, Jara says, she has tried unsuccessfully to secure support from regional authorities for finding a new source of water for the town. “Water is the main source of life,” she said. But “there’s a lot of government neglect over water.” Image by Marco Garro. Peru. A scientist with Peru’s National Institute of Glacier and Mountain Ecosystem Research (INAIGEM) dips a monitoring device into wetlands below the Pastoruri peak in the Cordillera Blanca mountain range. INAIGEM is studying how Andean wetlands purify water in order to design bioremediation projects for areas affected by acid rock drainage. Image by Marco Garro. Peru.
