There’s an interesting range of information available on the net relating to controlling algae with barley straw. The UK Centre for Aquatic Plant Management have developed a number of methods of dealing with aquatic and riparian plants, including a novel method of controlling algae. They have published a report describing the application of barley straw to water. The method has had widespread international testing and has proved to be very successful in most situations with no known undesirable side-effects. It offers a cheap, environmentally acceptable way of controlling algae in water bodies ranging in size from garden ponds to large reservoirs, streams, rivers and lakes.
The Maryland Aquafarmer has researched the use of barley straw to control pond algae and their findings are inconclusive. In laboratory studies, some types of algae could be controlled effectively by barley straw extracts, but the main target, green mat-forming algae, did not seem to be inhibited. However, barley straw did control several species of microscopic algae that often cause unusual odors or flavor in pond-cultured products. Follow-up studies found that some dinoflagellates – the single-celled phytoplankton that have been associated with fish death – are inhibited by barley straw.
Further to using barley straw to inhibit odor causing algae, a two-year project jointly funded by Australian Pork Limited and the Queensland Department of Primary Industries and Fisheries found that supported barley straw covers were effective in reducing odour emissions by up to 90% from anaerobic piggery effluent ponds.