Algae cause a number of problems in organized water systems. They impede flow in drainage systems, pumps and dams, interfere with navigation, fishing and other forms of recreation, cause taint and odour problems in potable waters, block filters and, in some cases, create a health hazard to humans, livestock and wildlife. These problems are increasing because nutrient concentrations in water are rising as a result of human activity and natural processes. Unicellular algae are difficult to control by methods used for other aquatic plants due to their small size and rapid growth. Algae are sensitive to herbicides, but this approach is unpopular in some waters because of the impact on the environment or human health and aquatic populations. Furthermore, herbicides destroy more plants, so the regrowth of algae is not restricted by competition from higher plants and the problem gets worse in subsequent years. The application of barley straw in water was tested in a wide range of situations in many countries around the world and has proved very successful in most situations with no known adverse side effects. During the process of decomposition, barley straw releases compounds in water that prevent the growth of algae. This application provides a cost effective, environmentally friendly way to control algae in water bodies ranging in size from garden ponds to large reservoirs, streams, rivers and lakes. Despite the simplicity of the idea, experience has shown that there are some basic rules that must be followed to ensure the success of barley straw for the above-mentioned purposes. The aim of this paper is to provide practical advice on the optimal ways of using barley straw for algal growth control in organized water systems.