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N.C. Lake Management Society

The North Carolina Lake Management Society encourages members to submit appropriate blog articles. Please keep the articles relevant to North Carolina lakes, ponds and stormwater devices. Visitors are welcome to comment on articles. 

Cyanobacteria... What?!

March 05, 2020 11:40 AM | Anonymous

Until recently, this surface film was considered a form of “blue-green algae”. We now know that there is no such thing as “blue-green algae”. Blue-green algae are now classified as bacteria and are correctly called cyanobacteria. As bacteria, they are mobile and can rise and sink through the water column. They have chlorophyll and can produce food for themselves through photosynthesis. Possible colors range from yellow to red to violet to green to deep blue, blue-green, gray and black.

Probably the oldest living forms of life, cyanobacteria are not very well understood. They exist everywhere. Nevertheless, nuisance blooms are increasingly troublesome throughout the Southeast. Cyanobacteria blooms are nuisances because they can be ugly, smell bad and can produce toxins. Sometimes the toxins have been associated with deaths of fish living in infested water or livestock and pets drinking the water. The toxins are increasingly linked to some chronic diseases. The blooms are usually not very stable and often crash in a relatively short period of time.

Unlike desirable plankton, cyanobacteria do not contribute significant amounts of dissolved oxygen. Cyanobacteria reproduce relatively slowly, usually about 1 time per day. Dead decomposing cells consume available dissolved oxygen. They are also not good oxygen producers like green plankton algae. The slow recovery of low oxygen levels contributes to occasional fish kills. Excessive blooms are not likely in lake and ponds that are routinely managed. We usually see short-lived thin surface films that are simply unattractive.

Because of potential toxicities, cyanobacteria are very important to aquatic resource managers. Currently being diligently researched are the physical/chemical and biological factors that encourage blooms and may potentially provide control. The factors include:

Physical factors:

           Agitation – 

Flushing, mixing and turbulence all may reduce cyanobacteria growth and reproduction. If water flushes through the lake faster than the nuisance can bloom, problems are reduced. If mixing can overcome the ability of the cyanobacteria to maintain its position in relation to light and available nutrients, growth is reduced. Shear turbulence can disrupt colonies and break up filaments. Aeration with fountains, and even diffused bubbles, can significantly reduce surface film formation.

            Shading – With limited light available, photosynthesis is inhibited. The concentration of the bloom and the composition of the species present are affected by the amount of light available and the depth of light penetration through the water. Shading can be effective for reducing numbers. However, the organisms ability to rise to the water surface may reduce the effectiveness of shading. 

            Temperature – Warm water temperatures, above 80oF., are associated with cyanobacteria blooms. Warm water is less dense than cooler water. Therefore, the warm water actually “floats” on top of denser cooler waters down deep causing stratification allowing surface water to warm dramatically. Through contact with the air at the surface of the water, nitrogen and carbon dioxide can be used by cyanobacteria as nutrient sources.

Chemical factors:

            Excess nutrients - High levels of nitrogen and particularly phosphorus are associated with cyanobacteria blooms. If the nutrients are reduced for months and years, blooms have been shown to diminish. Reducing nutrient inputs is one of the most effective control techniques. 

           pH – Low pH (acidic water) tends to inhibit growth of cyanobacteria. When the pH is above 8.0 problems increase. Regular additions of lime can buffer the pH and reduce high pH conditions.

            Salinity (or salt content) – Although cyanobacteria occur in salt water, research shows some species causing problems in fresh water may be controlled by 1 – 5 parts per thousand of salt. Therefore, each acre-foot of water would require 270 – 1,350 pounds of salt. Adding salt may only be practical in small ponds without much flow through. 

           Iron – Apparently, cyanobacteria are capable of out-competing some algae for limited levels of iron. When high nitrogen and phosphorus levels exist in the lake, adding iron may encourage the growth of desirable green algae. Research is continuing but adding iron is not a widespread control technique.  

Aquatic algaecides - Algaecides are chemicals that kill algae. Several formulations are available. Peroxide based algaecides may provide somewhat selective cyanobacteria control. Selection of the appropriate product, method of application, licensing requirements, existing weather and water conditions as well as many other factors complicate algaecide use. 


          Fish – Tilapia are fish that eat algae and will grow while eating cyanobacteria. However, the fish are tropical and will die when water temperatures drop below about 50oF. Therefore, in North Carolina they have to be stocked each spring. We have found that if we stock 50 – 100 fish per acre in the Spring, they can effectively control nuisance growth of some algae and appear to have reduced cyanobacteria issues in some ponds we manage. Recently the North Carolina Division of Inland Fisheries has restricted stocking tilapia in this state since they are not a native species. They are worried the fish will adapt to living in cooler water and may survive a warm winter. Sterile triploid grass carp eat may types of aquatic vegetation including some species of algae, but cannot filter out most types of cyanobacteria. Sterile grass carp are allowed in North Carolina but stocking may require a permit.  

            Beneficial bacteria concentrates: Beneficial bacteria/enzyme concentrates may compete with cyanobacteria for available nutrients. Probiotic and catalyst products are becoming popular for improving water quality in smaller ponds and stormwater devices. Although enormous numbers of bacteria occur naturally in lakes and ponds, these intentionally high concentrations of specific bacteria are showing beneficial results. An important factor is bottom "muck" organic sludge may be digested reducing nutrient cycling. "Bubbler" aeration and circulation appears to significantly improve effectiveness.   

            Barley straw: This has been used for “clarifying” ponds in Europe for generations and its use spread to the 

United States. It isn't widely used but there is evidence that as the straw decomposes in water substances are released that inhibit some algae growth.   

All of these factors and tools are considered cyanobacteria control activities. The most apparent surface film types of cyanobacteria usually represent a very small volume of material in lakes/ponds. If you could strain it out, it would only be a “handful”. It is simply very noticeable. Noxious blooms of very high volumes of cyanobacteria make the news and certainly cause important problems. However, smaller populations of these persistent species are often present without causing significant problems. We believe many times routinely treating cyanobacteria with chemicals simply makes it persist longer. Often we find that if the property owner is willing to live with it for a week or two, it will go away.   

Foster Lake & Pond Management provides the full range of lake, pond and stormwater management services and products. These include: construction, repairs, maintenance, certified inspections, fish stocking, fisheries management, lake mapping, vegetation management, docks, fountains and aeration.

We have provided aquatic and stormwater solutions to our North Carolina customers for over 38 years. Call us at: 919-772-8548 or visit:

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