Iloilo City, a highly urbanized city in the Philippines, experiences intensified climate change impacts due to the Urban Heat Island (UHI) phenomenon, one of which is the significant increase in temperature. To mitigate UHI, recent studies investigated the cooling effect of water bodies due to its higher rate of evapotranspiration compared to green spaces. This study aims to spatiotemporally assess the Urban Cooling Island (UCI) effect of Iloilo River and adjacent wetlands on the surrounding microclimate using geospatial techniques. Landsat images were processed to generate land surface temperature (LST) and land cover layers of the study area for the years 1994, 1998, 2003, 2005, 2013, 2016, and 2019. UCI Scale (influence range of the cooling effect), Temperature Difference (difference in temperature between water space and the area within the UCI scale), and UCI Intensity (temperature gradient within the UCI scale) were calculated using multiple-ring buffers with 50-m interval to quantify variations in cooling effect of the water space at distinct surrounding regions over a long time period. Results of the study show that wetland area has a weak negative relationship with the UCI indices which could mean that cooling effect is not solely dependent on wetland size, while moderate to very strong negative correlations were calculated between temperature difference and precipitation (r = −0.48 to −0.82). Furthermore, rapid expansion of built-up areas at different sections along the river have resulted to reduced UCI scale (r = −0.37 to −0.75) and stronger cooling intensity (r = 0.55 to 0.84).