In this activity (on pages 36-39), learners make a model of a watershed out of paper, then run water down the mountain to simulate how rainfall and pollution affect watersheds. Learners are introduced to the ABCs of runoff—how agricultural runoff, bulldozers, chemicals and human debris impact lakes, streams and rivers in urban as well as suburban areas. Water-soluble colored markers are used to represent rivers and these pollution sources. The "Think It Over" section at the end encourages learners to reflect on what they wash down their drains at home.