We identified ± 150 glacial lakes in the Poiqu River basin (central Himalayas), and we explore the changes in five lakes over the last few decades based on remote sensing images, field surveys, and satellite photos. We reconstruct the lake basin topography, calculate the water capacity, and propose a water balance equation (WBE) to explain glacial lake evolution in response to local weather conditions. The WBE also provides a framework for the water balance in rivers from glacierized sources.