Freshwater sources and oceans have an amazing natural ability to break down some waste materials, but not in the quantities discarded by today' s society. The overload that results eventually puts the ecosystem out of balance. Sometimes nature itself can create these imbalances. But most often our waterways are being polluted by municipal, agricultural and industrial wastes, including many toxic synthetic chemicals which cannot be broken down at all by natural processes. Even in tiny amounts, some of these substances can cause serious harm to the plants and animals that live in or near the water. .
