Another way to measure the size of a river is by the amount of water it discharges. Using this measure the Mississippi River is the 15th largest river in the world discharging 16,792 cubic meters (593,003 cubic feet) of water per second into the Gulf of Mexico. The biggest river by discharge volume is the Amazon at an impressive 209,000 cubic meters (7,380,765 cubic feet) per second. The Amazon drains a rainforest while the Mississippi drains much of the area between the Appalacian and Rocky Mountains, much of which is fairly dry.