Urban expansion has intensified the heat-island effect, and the negative impact on the natural environment has gradually become considerable. However, urban lakes can significantly alleviate the heat-island effect caused by urbanization. Based on four-phase multispectral remote-sensing images during 2005–2020, 17 lakes in the main and surrounding urban areas of Hefei, China, were selected as the objects of our research. Each lake’s cooling intensity and distance were calculated; cooling-efficiency data for different lakes were compared and analyzed considering lake areas and regional differences. The following conclusions were drawn: (1) The central temperature of the lakes correlated positively with cooling intensity (R = 0.55, P < 0.01) but negatively with cooling distance (R = −0.28, P < 0.05); the area of the lakes was significantly positively correlated with cooling distance (R = 0.49, P < 0.01) and weakly positively correlated with cooling intensity. When a lake area reached a certain threshold, its cooling intensity tended to stabilize. (2) The lakes around the urban area were far away from the main urban area where the heat-island effect was most concentrated, the ability of absorbing the high surface temperature caused by the heat-island effect was limited, the cooling-intensity and cooling-distance efficiency were less than those of the main urban lakes. (3) With urban expansion and the intensified urban heat-island effect, the cooling-intensity efficiency of lakes in the main urban area gradually increased, whereas the cooling-distance efficiency of lakes decreased.