Robert Earhart, right, a park ranger for the U.S. Army Corps of Engineers Nashville district, organizes a game at Old Hickory Lake with students of Hawkins Middle School, during Environmental Awareness Day in the Rockland Recreation Area at Hendersonville, Tenn., May 7, 2013. Earhart helped the students understand the term "carrying capacity," which is the number of animals a given area of land or water can support over time. (U.S. Army photo by Leon Roberts/Released)