The rainwater then seeps into the soil which has become porous due to the action of decomposing insects and the root network of plants. Water filters slowly through the soil until it eventually reaches surface waterways, such as streams or lakes. Water naturally moves slowly through this system, continuously replenishing streams and preventing extreme cycles of flood and drought. The forest cover protects the soil from erosion, so the water that flows is clean. If the watershed has been deforested, there is less vegetation to shade the soil and to reduce the erosive force of the rain.
Water runs swiftly off the mountains taking precious topsoil with it.
The water supply dries up in summer because there is no longer the natural mechanism of storage and slow release. Drinking water is clouded with silt, and contaminated with parasites from the waste of humans and livestock that live or work in the watershed. Runoff is immediate because the watershed has lost the ability to store water. Rivers are thick with mud, and flooding occurs frequently and fiercely. In the Bay Islands off the Caribbean coast, soil from deforested hillsides is washed into the sea where it slowly chokes the beautiful coral reefs that bring the country international acclaim.