The synergistic cooling effects of urban blue-green spaces are increasingly a central focus in urban thermal environment research. This study examines the synergistic cooling effects of blue-green spaces in four typical waterfront residential areas in Nanjing, China. Using drone-acquired data on blue-green spaces combined with numerical simulations, we analyzed the cooling performance in the study areas. The results indicate that: (1) The average cooling intensity of blue-green spaces showed a trend of rising first and then falling during 07:00–19:00, reaching a peak at around 15:00 (1.52 ℃). The introduction of water elements significantly enhanced the cooling intensity in waterfront residential areas. The cooling intensity of coupled blue-green elements was higher than that of single vegetation elements, indicating a notable synergistic cooling effect of blue-green spaces. Additionally, the cooling intensity of single planar water bodies was higher than that of dispersed or complex-shaped water bodies, and water bodies with greater width exhibited higher cooling intensities. (2) During the daytime, the cooling intensity was generally higher within and around water bodies within a certain distance, and it gradually decreased as the distance from the water bodies increased. Under the influence of prevailing wind directions, the cooling intensity is higher in the leeward area around water bodies as opposed to the windward areas. The wider the water body, the higher the cooling intensity within it; however, the cooling intensity around water bodies showed minimal correlation with water body shape or width. In the evening, the spatial distribution of cooling intensity was generally similar to that during the daytime, but the overall cooling intensity was significantly reduced. Notably, narrow linear water bodies exhibited relatively higher cooling intensity during this period. (3) During the daytime, single planar water bodies exhibited the largest cooling range, covering up to 95.52% of the study area. Dispersed or complex-shaped water bodies had the longest cooling distance, extending up to 248 m. This indicates that the cooling range is strongly correlated with the shape and width of the water body, whereas the cooling distance is more closely associated with the number of surrounding trees. Both the cooling range and cooling distance are significantly influenced by wind direction, with larger values observed in the downwind areas of water bodies. The cooling effects of four different water body configurations were most evident within a distance of 7–32 m from the riverbank. Compared to daytime, narrow linear water bodies exhibited superior cooling performance in the evening. These insights offer valuable scientific guidance for the development of urban waterfront areas.