The global boom in hydropower dam construction is driven by the need to meet increasing energy demands, address climate change, and close the electricity access gap. At least 3,700 major dams, each with a capacity of over 1 MW, are either planned or under construction, primarily in emerging economies. This expansion is expected to increase global hydroelectricity capacity by 73%, to about 1,700 GW. However, this growth will not fully meet the rising electricity demand and may not significantly reduce greenhouse gas emissions or resolve social conflicts. The construction of these dams is also expected to reduce the number of free-flowing large rivers by about 21%. The rapid growth in hydropower production, which currently accounts for 80% of renewable energy, is a response to the Rio+20 targets and the need to meet Kyoto-compliant energy resources. The economic, ecological, and social impacts of this boom are significant, and a comprehensive global inventory of future hydropower dams is necessary to identify hotspots, calculate river discharge impacts, and estimate cumulative river fragmentation. The data compilation, based on over 350 references, provides a conservative estimate of the number of future hydropower dams and their potential environmental and social consequences.The global boom in hydropower dam construction is driven by the need to meet increasing energy demands, address climate change, and close the electricity access gap. At least 3,700 major dams, each with a capacity of over 1 MW, are either planned or under construction, primarily in emerging economies. This expansion is expected to increase global hydroelectricity capacity by 73%, to about 1,700 GW. However, this growth will not fully meet the rising electricity demand and may not significantly reduce greenhouse gas emissions or resolve social conflicts. The construction of these dams is also expected to reduce the number of free-flowing large rivers by about 21%. The rapid growth in hydropower production, which currently accounts for 80% of renewable energy, is a response to the Rio+20 targets and the need to meet Kyoto-compliant energy resources. The economic, ecological, and social impacts of this boom are significant, and a comprehensive global inventory of future hydropower dams is necessary to identify hotspots, calculate river discharge impacts, and estimate cumulative river fragmentation. The data compilation, based on over 350 references, provides a conservative estimate of the number of future hydropower dams and their potential environmental and social consequences.