A new study published this week in the journal Nature shows that while human-controlled freshwater sources make up a minimal portion of the world's ponds, lakes, and rivers, they are responsible more than half of all changes to the Earth's water system. Using NASA's ICESat-2 satellite, researchers monitored more than 227,000 bodies of freshwater–ranging in size from the Great Lakes to tiny ponds over period spanning roughly a year and a half. Researchers found that 57% of global seasonal water storage variability occurs in human-controlled reservoirs. "This large proportion is even more striking when one considers that reservoirs only account for 3.9% of the 227,386 lakes analyzed in this study," said UC Berkeley professor Sarah Cooley, the study's lead author. "While the water cycle is generally portrayed as a natural process, our finding that humans are responsible for the majority of seasonal surface water storage variability shows that we are now a key regulator of the water cycle."