A widespread decline in dissolved oxygen (DO) has been observed in rivers, temperate lakes, and oceans, yet the impacts of climatic warming on global lake deoxygenation remain unclear. Here, we train data-driven models using climatic data, satellite images, and geographic factors to reconstruct surface DO and quantify the climatic contribution to DO variations in 15,535 lakes from 2003 to 2023. Our analysis indicates a continuous deoxygenation in 83% of the studied lakes. The mean deoxygenation rate in global lakes (?0.049 milligrams per liter per decade) is faster than that observed in the oceans and in rivers. By decreasing solubility, climatic warming contributes 55% of global lake deoxygenation. Meanwhile, heatwaves exert rapid influences on DO decline, resulting in a 7.7% deoxygenation compared to that observed under climatological mean temperatures. By the end of the century, global lake DO is projected to decrease by 0.41 milligrams per liter (4.3%) under SSP2-4.5 and 0.86 milligrams per liter (8.8%) under SSP5-8.5 scenarios. Both long-term climate change and short-term heatwaves have a profound impact on dissolved oxygen levels in global lakes.