2The longest river in the United States isn't the Mississippi River--that's the Missouri. But, the Missouri is part of the huge Mississippi River system that's truly a natural wonder! It contains 250 tributaries in all. Readers learn even more fun facts about the Mississippi River and its system of waterways in this volume. With content supporting both social studies and science curricula, the accessible text covers geography as well as conservation. Full-color photographs of the mighty Mississippi, its wildlife, and the way people have made their homes around it are featured.