Abstract
Certain algae have direct benefit as food or fertilizer. Excessive growths of algae in fresh water, however, reduce water quality and make it less suitable for drinking or amenity use. They also present difficulties in freshwater fisheries, in industrial cooling systems, and in drainage and irrigation of agricultural land. In salt water, certain algae cause fouling of ships’ hulls. Although some control is possible by means of chemical algicides there are many problems still to be solved.