The Energy Department said it worked with researchers at the Oak Ridge National Laboratory to examine the electric power potential in the estimated 3 million rivers and streams in the country.
It found more than 65 gigawatts of power could be generated from U.S. waterways, with most of that potential existing in states west of the Mississippi River.
Energy Secretary Ernest Moniz said the findings are unprecedented.
"The United States has tremendous untapped clean energy resources and responsible development will help pave the way to a cleaner, more sustainable and diverse energy portfolio," he said in a statement Tuesday.
Hydropower accounts for 7 percent of the electricity generated in the United States. The Energy Department said hydropower is the largest source of renewable electricity in the country.
The estimate of 65 GW means there's more potential new hydropower available than is currently available on the U.S. grid.