Cyanobacteria (formerly called “blue-green algae”)

Our customers and clients are concerned about the cyanobacteria (formerly called blue-green algae) surface film on their lakes and our efforts concerning control. We have recognized an increasing problem over the past several years and have put extraordinary effort into control. Our results in trying to control the problem have not always been consistent. This will provide an opportunity to explain the problems we are having.

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 actually 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 form of life, cyanobacteria are not well understood. They exist everywhere. Nevertheless, nuisance blooms are increasingly troublesome throughout the Southeast. Cyanobacteria blooms are nuisances because they are ugly, smell bad and can produce toxins. Rarely the toxins have been associated with deaths of fish and livestock drinking the water. The blooms are 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, 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 we manage. As a result of our routine management, you are not likely to see fish kills and toxicity. We usually see short-lived thin surface films that are simply unattractive.

Controlling cyanobacteria is very important to us. We’ve diligently researched the physical/chemical and biological factors that may potentially provide control. The factors include:


Agitation – Cyanobacteria like still water. Flushing, mixing and turbulence all reduce cyanobacteria growth. If water flushes through the lake faster than the nuisance can bloom, problems are reduced. If mixing can overcome the ability of the bacteria 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 (Airmax and Aquamaster), and even diffused bubbles (Airmax and AquaAir), 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. Lake colorants are one way to provide shading (FLPM Private Label Pond Dye).

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” 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 food sources. Disturbing the stratification with circulation, such as with diffused air aeration (Airmax and AquaAir), or adding well water can lower the surface water temperature.


Excess nutrients - High levels of nitrogen and phosphorus are associated with cyanobacteria blooms. If the nutrients are reduced for months and years, blooms have been shown to diminish. Research has shown high phosphorus levels relative to nitrogen levels in pond water encourages cyanobacteria. Chemically binding the phosphorus with alum or lanthanum (Phoslock) can make it unavailable.

pH – Low pH (acidic water) tends to inhibit growth of cyanobacteria. When the pH is above 8.0, cyanobacteria problems increase. Regular additions of lime (FLPM Calcis (lime) application video, Calcis by Biosafe Systems ) can buffer the pH and reduce high pH conditions.

Salinity (or salt content) – Although cyanobacteria occur in salt water, research shows the nuisance species can be controlled by 1 – 5 parts per thousand of salt. Therefore, each acre-foot of water would require 270 – 1,350 pounds of salt. We have been very unimpressed with results from using salt for control.

Iron – Apparently, cyanobacteria are capable of out-competing 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. We are still trying to learn more about possibly adding iron.


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, they have to be stocked each spring. We have found that if we stock 50 – 100 fish per acre in the Spring, they will effectively control nuisance growth of some algae. Tilapia reproduce abundantly. However, availability is limited and predators may eat small fish. The fish cannot be stocked until the water temperature is consistently above 70oF in the spring. We have had trouble maintaining effective populations in some lakes and ponds. Recently, the North Carolina Division of Inland Fisheries has asked us not to stock any more tilapia in this state. They are concerned because they are not native fish and may someday adapt to colder water and be able to survive a warm winter.  

Beneficial bacteria/enzyme concentrates - Although results are somewhat inconsistent, beneficial bacteria concentrates (Naturalake Biosciences ) may compete with cyanobacteria for available nutrients. These concentrates may be dry powders or liquid formulations with up to 25 billion viable microorganisms and 18 billion spores per gram. A bran carrier may be used that contains a “conditioned” media that serves as nourishment when the powder is mixed with pond water. Supposedly, this allows the bacteria to double every 20 minutes. Furthermore, the spores germinate to the vegetative, active growing form.

Barley straw- We are not allowed to claim barley straw might “control” algae growth since it has not been registered as a pesticide by the United States EPA. However, its popularity for “clarifying” ponds in Europe for generations has spread to the United States. We began putting barley straw in lakes and ponds in 1999. We generally recommend 3 bales (approximately 40 pounds each) per acre twice per year. The results are inconsistent. We tend to get better results in small ponds less than 1 acre in size. The bales of straw can be difficult to obtain, store, transport and deploy in lakes and ponds. Therefore, the demand is very limited.   

New Technologies

Low P lawn fertilizers Several manufacturers now produce low phosphorus or no phosphorus lawn fertilizers that should reduce phosphorus runoff into lakes and ponds.

Ultrasonic Devices – Using high frequency sound waves that are not harmful to fish, other aquatic organisms, humans or other animals can disrupt some types of cyanobacteria. These devices use very little electricity, so solar options are very practical where no power exists. The devices are not widely utilized in lake and pond situations but research is continuing.

Algaecide with phosphorus binder – It makes sense to bind phosphorus from decaying algae and cyanobacteria so it is not available for future growth (SeClear). Algaecides will continue to be a major control method for nuisance populations of cyanobacteria. An algaecide with lanthanum will kill the organisms while not allowing the release of phosphorus that might encourage additional growth. 

All of these factors are considered in our control activities. The surface film types of cyanobacteria actually 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. We are fairly successful sometimes at controlling the volume, but we have not been able to entirely eliminate the persistent species. We believe many times treating cyanobacteria with chemicals simply makes it persist longer. Often we find that if the client is willing to live with it for a week or two, it will go away.

We don’t claim to be able to control every instance of cyanobacteria in your lake or pond. But, we promise to do everything we can to stay knowledgeable about control methods and keep our tool box full of as many tools as become available.


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