A modeling analysis indicates that both climatic warming and short-term heatwaves contributed to a profound decline in dissolved oxygen in more than 15,000 lakes worldwide from 2003 to 2023.

Yibo Zhang and colleagues found continuous deoxygenation in 83% of the 15,535 lakes they studied, and the average deoxygenation rate in these global lakes is faster than that observed in both oceans and rivers. Declining levels of dissolved oxygen can severely disrupt lake ecosystems, limiting habitat and productivity for certain species and impacting food security and coastal economies as a result. Deoxygenated lakes also have increased emissions of the greenhouse gas nitrous oxide, which can exacerbate climate warming.

While widespread declines in dissolved oxygen have been observed across water bodies in recent decades, the exact drivers behind this decline in lakes have been unclear. Zhang et al. created models using climatic data, geographic factors, and satellite images to reconstruct lake surface dissolved oxygen levels and quantify how long-term climate change and heatwaves affect these levels. They concluded that climatic warming contributes 55% of global lake deoxygenation, by reducing oxygen solubility.

Heatwaves lead to 7.7% additional deoxygenation compared with deoxygenation under average temperatures – and 85% of the lakes in the study experienced a gradual increase in the number of heatwave days per year during the study period. If these trends continue, the authors note, lakes such as Lake Victoria in East Africa could experience prolonged periods of deoxygenation that would severely affect fish growth and food production.