In a study of the energy-producing potential of untapped US dams, Oak Ridge National Laboratory researchers found that 54,000 dams not currently used to generate power have the capacity to generate more than 12 gigawatts, enough to power more than 4 million homes. ORNL and Idaho National Laboratory researchers conducting a hydropower resource assessment for the Department of Energy calculated that the 100 dams with the highest energy potential could generate 8 gigawatts of power. The top 10 power-generating dams are along the Ohio, Mississippi, Alabama, Tombigbee, Arkansas and Red rivers. Equipping existing dams with power-generating plants avoids additional environmental impacts because the dams are already operating. Additionally, installing hydropower won't change the timing of flows released from the dams.