Climate change and El Niño Southern Oscillation influence on mixing regime and water quality in a deep tropical mountain lake

Abstract Climate change alters lake functioning, water quality, and aquatic biota; yet our understanding of this process is poor for deep tropical mountain lakes. A 15‐yr dataset (2010–2024) from Lake Atitlán, Guatemala, revealed climate change impacts on a tropical lake ecosystem and showed a warming trend of 0.34 ± 0.14°C per decade that intensified during warmer phases of the El Niño‐Southern Oscillation. Increased air temperatures and reduced wind speeds were related to shallower thermocline depths and stronger stratification that prolonged anoxia and deteriorated deep‐water quality during stagnation. Years with complete mixing released phosphorus to the surface, created low dissolved inorganic nitrogen‐to‐phosphorus ratios associated with cyanobacteria blooms (notably in 2011–2013, 2015, and 2018), and altered water quality. These findings highlight the influence of climate change on physicochemical dynamics that modify ecosystem health and emphasize the need for ongoing research to sustain ecosystem services and prepare vulnerable populations for future scenarios.