The Trans-Alaska Pipeline can transport and pump up to 2.1 million barrels (330,000 m3) of crude oil per day, more than any other crude oil pipeline in the United States. Additionally, substantial coal deposits are found in Alaska's bituminous, sub-bituminous, and lignite coal basins. The United States Geological Survey estimates that there are 85.4 trillion cubic feet (2,420 km3) of undiscovered, technically recoverable gas from natural gas hydrates on the Alaskan North Slope. Alaska also offers some of the highest hydroelectric power potential in the country from its numerous rivers. Large swaths of the Alaskan coastline offer wind and geothermal energy potential as well.
Alaska's small rivers have potential for what environmentally friendly type of energy production?