Even as the world’s supply of clean water continues to dwindle, current Earth observation systems cannot adequately monitor long-term changes in the global water system and the impact they may have on people, climate, and biodiversity. Yet the world’s supply of clean water continues to dwindle. Because the amount of available freshwater is affected by many variables, GEOSS will help track these variables by filling in information gaps, integrating data sets from various monitoring systems, developing better forecasting models, and disseminating the results to a wider range of decision-makers. Holding one-fifth of the Earth’s freshwater, the Great Lakes will benefit greatly from such activity. Coupled with research and other resources, improved remote sensing and in situ observations can lead to improved water quality, better control and prevention of invasive species, critical wetlands banking, and healthier fish and wildlife habitat.