I have received many calls here lately about the blue-green algae scare. What is growing in my ponds? What can I do about it? And is it toxic to my dogs, cows, and kids? Hopefully this article will answer most of your questions about the subject and put your mind at rest.

Blue-green algae are also called cyanobacteria because they are biologically similar to bacteria in many ways. As single cells, large colonies and filaments, blue-green algae grow in a wide variety of conditions and can become dominant in nutrient-rich water bodies. One characteristic of these cyanobacteria is their ability to form blooms so thick it appears that blue-green paint covers the surface of the water. Two forms found in Texas are known to produce substances which cause taste and odor problems in water supplies. In some cases, blue-green algae, particularly Anabaena and Microcystis (both found in Texas), can produce toxins that are poisonous to fish and wildlife that drink water contaminated with the toxins. Fish kills have occurred in private stock ponds as a result of blue-green algal blooms and there have been a few reports of livestock dying from drinking water contaminated with blue-green toxins. In addition to toxicity to fish and wildlife, there are documented cases of blue-green algal toxins harming humans through the consumption of poorly treated waters.

The Texas Parks and Wildlife Department responds to harmful algal blooms when there have been impacts to fish or wildlife but does not conduct regular water quality testing or monitoring of water bodies in lieu of any reported fish and wildlife kills. Any ongoing water quality testing or monitoring would be conducted by the governing water controlling authority that manages a particular area. It is recommended that one avoid areas with visible cyanobacterial or algal concentrations and/or scums in the water as well as on the shore. Direct contact and swallowing appreciable amounts are associated with the greatest health risk.

The active ingredients that have been successful in treating Blue-Green algae include: Copper complexes (rated: excellent) (Cutrine Plus, K-Tea, Captain and Clearigate); alkylamine salts of endothall (rated: good) (Hydrothol 191); and sodium carbonate peroxy-hydrate (rated: good). Copper Sulfate or “blue stone” is probably the most commonly used algal treatment because of its availability and low cost. Copper sulfate comes in several forms depending on how finely it is ground. Smaller crystals will dissolve easier than larger crystals. In very hard water it is difficult to use copper sulfate because it binds with the calcium, precipitates out of solution and renders the copper ineffective as an algaecide. Other copper products to use include Cutrine Plus, K-Tea, Captain and Clearigate. Another good product is Airmax Algae Defense.

One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletion can kill fish in the pond. If the pond is heavily infested with weeds, it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion also. Non-toxic dyes or colorants prevent or reduce aquatic plant growth by limiting sunlight penetration, similar to fertilization. Some examples of non-toxic dyes and other products include but are not limited to: Aquashade, Blue Springs, Crystal Blue. A lab that tests for toxins is difficult to locate. I would start with LCRA Environmental Laboratory Services at www.lcra.org.

Marty Morgan is Cooke County Ag Agent for the Texas A&M AgriLife Extension Service. Reach him at 940-668-5412 or marty.morgan@ag.tamu.edu.

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