Abstract Natural lakes and artificial reservoirs are important components of the Earth system and essential for freshwater, food, and energy. Relatively little is known about the variations of lake and reservoir surface area globally. For the first time, this study presents the global variation of lake and reservoir surface areas for all water bodies larger than 1 km2. Using radar remote sensing, we found that global aggregate area variations were only 2% of total surface area over a 3 year period. When considering the total surface area of shoreline regions that transition between land and water, these variations equaled 20% of total lake and reservoir surface area, largely driven by variations of smaller water bodies. Additionally, surface areas of reservoirs tends to be more variable than the surface area of lakes of similar size. The large surface area variations evidenced here, could have a previously underappreciated impact on the Earth System.