The Mississippi River is the fourth longest river in the world and empties 600,000 cubic feet of water per second into the Gulf of Mexico. The Native Americans relied on it for food, water and transportation -- and today we rely on it for many of the same things. Twenty-five percent of all the fish species in North America live in the Mississippi, and the river’s basin produces 92 percent of our nation’s agricultural exports. But the river hasn’t always looked the way it does today (see David Gessner's ode in our Spring 2011 issue, "Free the Mississippi"). Today’s Mississippi is the result of centuries of engineering, and the river’s history is one of constant struggle between human technology and natural force.