Barley straw may be an effective way to prevent algae from reproducing, but once algae is established, barley straw is not effective in eliminating algae. Research using barley straw as a way of controlling algae growth was first conducted in England (1). Similar research studies in the United States have not been as successful at showing that using barley straw is an effective method of controlling algae growth. Some of the reasons for this are unknown, while recent research suggests that barley straw shows promise as an effective control for certain types of algae, but not others.(2)

Microorganisms responsible for breaking down barley straw, such as fungi and bacteria, are naturally occurring in soils, ponds, and lakes. There are two ideas as to how microorganisms and barley straw help prevent algae growth:

1) Microorganisms breakdown barley straw and produce chemical compounds that may prevent algae from reproducing.(3)

2)Certain microorganisms break down barley straw, which releases more carbon into their environment. This newly available carbon is now available to consume by other microorganisms that were previously limited by carbon. While microorganisms use the newly available carbon to grow and reproduce, they also take up more of the nutrient phosphorus, which limits the availability of algae to grow and reproduce. (3)

To use barley straw as a means to prevent algae in water, barley straw must be well distributed near the water surface several months before bloom. Water must also be well aerated for best results. When using barley straw in ponds, homeowners may want to use some kind of supplemental aeration to maintain enough oxygen in the water for fish and decomposing microorganisms.

Find more useful information and instructions on using barley straw for algae control at:
Algae Control with Barley Straw

--------References-----------
1) T Newman, J. 1997. Control of Algae with Barley Straw. Information Sheet No. 3. Institute of Arable Crops Research, Center for Aquatic Plant Management. Berkshire, UK.

2)Barley Assessments of the Use of Barley Straw Hordeum vulgare to Supress Algae Growth in NW Oregon.

3) Geiger, S., Henry, E., Hayes, P., Haggard, K. 2005 Nov 1. Barley Straw-Algae Control Literature Analysis.

4)The Oregon Garden Wetlands. Barley Straw Algae Control Research. Barley Straw Algae Control Research