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Algae are microscopic, free-floating plants which comprise a critical component of a lake's food web. They are fed upon by tiny animals called zooplankton which are an important food source for fish. Algae color the water green or brown, and uncontrolled growth can lead to nuisance surface scums, poor water clarity, noxious odors and an overall reduction in the lake's recreational value. Excessive levels or "blooms" of algae occur when nutrients, especially phosphorus, are abundant. After taking steps to reduce the amount of phosphorus entering a lake, it may be desirable to control the algae growth directly. Typically this is accomplished by treating the lake with copper-containing compounds such as Cutrine Plusr or copper sulfate. These treatments are effective short-term controls of algae, but they are also toxic to nontarget organisms that are important food sources for fish such as zooplankton and insect larvae. Re-application of these chemicals is usually necessary several times each year and the long-term buildup of copper in the lake sediments is an environmental and health concern.
The Centre for Aquatic Plant Management (CAPM) in the United Kingdom is promoting a method of controlling algae that involves the application of barley straw to lakes. As the straw decomposes in the lake, it releases a chemical which inhibits algal growth. This method may be a good alternative to using copper-containing compounds since it is not known to have toxic effects on rooted aquatic plants, zooplankton, insect larvae or fish. It appears to be a cost-effective and environmentally acceptable way to control algae in ponds and lakes.