Some people use fertilizer on lawns to help them grow. When people use more fertilizer than their lawn needs, or if they fertilize just before it rains, a lot of fertilizer ends up in runoff and not on the lawn. You know what happens next… down the storm drain and into the river. Fertilizer helps things grow, but when it gets in water, it helps algae grow. Algae blooms can cause major problems in waterways because they use up oxygen needed by other river critters. What can people do who want to fertilize their lawn? Only use as much fertilizer as the lawn needs, and try not to fertilize before it rains.