Hydrosphere Contents

5. Aquatic Habitats

Open waters are at risk from pollution

The death of fish is often the first visible sign of polluted water

The death of fish is often the first sign of a pollution incident in a river or lake. The cause of the fish kills is usually deoxygenation of the water, which is a secondary effect arising from a chemical pollutant entering the river. Nitrates and phosphates, for example, are present in agricultural effluents, resulting in eutrophication. Salmon and other migratory fish can be greatly affected by low oxygen levels. Management of vegetation in lakes and standing bodies of water is necessary to avoid either too much or too little plant growth. Low growth is not a common problem. In situations where it does occur, it is usually possible periodically to add the limiting nutrient, such as phosphate, to the lake to encourage growth. New species can be introduced to the shores to encourage a greater biodiversity of both plant and animal species.

Which two chemicals can cause eutrophication?