The land drains into tributaries and tributaries flow into the river. As the water flows downhill, it moves over the land or drains through the soil. Along the way, water picks up woody debris, leaves, and needles that provide the foundation of food and shelter for aquatic life in streams. Water can also carry motor oil, fertilizer, pesticides, and eroded soil. Small actions like driving the car, fertilizing pasture, or even walking the dog can inadvertently pollute the watershed you live in. As the tributaries flow into the river, so do the pollutants. It all adds up.