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(Redirected from Blue-Green Algae)

By Colleen Henn


Blooms of Cyanobacteria, also known as blue-green algae, are affecting inland and coastal communities around the world. According to NOAA, harmful algal blooms have been reported in every U.S. coastal state.

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Cyanobacteria are aquatic bacteria, and are some of the oldest living organelles on Earth. Because these water-dwelling bacteria photosynthesize, they are also referred to as “blue-green algae.” Cyanobacteria can be found in many different environments, including freshwater and marine ecosystems. Despite being named “blue-green algae,” blooms may appear in many different colors including red, yellow, brown, blue, and green, and often form a scum on the water’s surface.

There are many different types of Cyanobacteria, but not all produce toxins. Microcystin and Anatoxin are two of the more common toxins that are produced by Cyanobacteria, and in high concentrations can be very harmful to other organisms living in the same aquatic environment. Under optimal conditions such as warm temperatures, sunlight and plentiful nutrients such as nitrogen and phosphorous, cyanobacteria can grow in localized blooms. When these blooms form toxins, which is increasingly becoming problematic in areas of high nitrogen concentrations, there are a whole host of public health concerns as drinking contaminated water, eating shellfish and or even swimming in affected waterways can cause serious health effects. For this reason, harmful algal blooms are monitored to protect drinking water and prevent recreational exposure.

Causes of Bloom Formation

To understand how and why harmful algal blooms form, it’s important to note that cyanobacteria tend to reproduce rapidly in water with the following conditions: elevated nutrient levels, high temperatures and still water.

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Numerous human activities increase the levels of nutrients present in bodies of water, especially nitrogen which is a source of energy for bacterial growth. Sources of nitrogen that affect waterways include agricultural, urban and residential runoff, and especially inadequately managed wastewater from either sewage or septic systems. Nitrogen pollution threatens the health of water all over the world. For a detailed example of how nitrogen affects waterways and surrounding communities, view this video about nitrogen pollution in Long Island, New York.

Scientists are also beginning to link the increased frequency of harmful algal blooms to climate change and human activity. Worldwide, these blooms are increasing in magnitude, frequency, and in geographical spread. With warmer temperatures associated with climate change, cyanobacteria are blooming in more northern latitudes. Stormwater associated with climate change induced high intensity rainfall, carries nitrogen and phosphorus into surface waterways. Because cyanobacteria also grow well in still water, blooms are becoming more frequent in rivers that have been dammed to create reservoirs.

With a rapidly changing climate, warmer weather, more intense rainfall, and pollution caused by human activity, we are perpetuating optimal conditions for harmful algal blooms. In high densities, these algae may discolor the water and outcompete other life forms.

Health Effects

There are numerous health and ecological effects associated with toxic cyanobacteria blooms. Humans are at risk to exposure while recreating in affected waters through ingestion, skin contact, and when airborne droplets containing the toxins are inhaled while swimming. Humans are also exposed to cyanobacteria when consuming shellfish from water bodies containing a high concentration of cyanotoxins. As stated by Markain Hawryluk with the Bend Bulletin, “microgram for microgram, the toxin is more deadly than cobra venom.”

Although humans are at risk of exposure, it is very hard for officials to track cases of human illness caused by harmful algal blooms because minor symptoms are overlooked. The effect of cyanobacteria on human health varies with the type of toxin present, its concentration, and the duration of exposure. The higher the concentration of cyanotoxin and the longer the exposure, the more severe the symptoms may be. Health effects usually occur when exposed to a high concentration, but some people may be more susceptible to developing symptoms.

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Skin contact with cyanotoxins can cause irritation of the skin (rash or skin blisters), eyes, nose and throat, and inflammation of the respiratory tract. Swallowing water containing high concentrations can lead to nausea, vomiting, abdominal pain and diarrhea. Effects on the liver and nervous system of animals and people have also been documented in severe cases.

Dogs, livestock and other animals that drink water from affected areas or lick their fur to clean it are at a much higher risk of toxins than humans. Animals usually drink from areas on the edges of affected water, where algae tend to accumulate. Livestock and pet deaths have occurred after these animals have consumed large amounts of toxic algal scum accumulated along shorelines.

Health Guidelines and Policies

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Currently, the Environmental Protection Agency has issued an advisory for the amount of cyanobacteria in drinking water, but criteria for recreation are still being developed. Due to the risk associated with recreational exposure to cyanotoxins, the EPA intends to develop criteria under the Clean Water Act (Ambient Water Quality Criteria). On December 12, 2016 EPA issued draft recreational water quality criteria and/or swimming advisories for the cyanotoxins microcystin and cylindrospermopsin. EPA has identified draft recommended concentrations of the cyanotoxins to protect human health while swimming or participating in other recreational activities in and on the water.

Although EPA is in the process of developing their cyanotoxin guidelines, some states have developed their own criteria for recreational exposure to cyanotoxins. Twenty-one states have implemented harmful algal bloom response guidelines when there is a bloom present. These guidelines are usually based on the visible presence of scum on the surface, cell count, and toxin (microcystin and anatoxin) levels. For example, the state of Massachusetts suggests avoiding contact with water when there are 14 micrograms of Microcystin per liter of water and anything greater than or equal to 70,000 cell count of cyanobacteria per milliliter of water. In addition to Microcystin, the state of Oregon releases a Public Health Advisory when four other cyanotoxins are above state-recommended limits.

Currently, toxin measurements require that samples be collected and analyzed in a laboratory, but one study shows that site-specific models could be developed to estimate and predict cyanobacterial blooms at freshwater sites given several predictor variables. “Models provide the opportunity for public health protection prior to exposure and allow users to be proactive rather than reactive.” These models provide an opportunity to predict where blooms may occur and therefore target priority areas to propose solutions.


The increased local and national coverage of the growing threat that cyanobacteria blooms and their toxins pose to recreation, public health, and local economies, has created in many locations the public awareness and political will to start solving water pollution problems. There are also ways all of us can take action at home to support clean water and prevent nutrient pollution from getting into local waterways and causing cyanobacteria to bloom.

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  • Maintain your cesspool or septic system. Septics should be inspected and pumped every 3 years, or every year if you live next to the water. Also make sure you aren’t pouring any harsh chemicals down the drain (cleaning supplies, paint thinners, etc.) as they interfere with the treatment of your wastewater. More about septic maintenance here.

  • Support efforts to connect properties to sewage treatment plants or advanced waste treatment technologies. Even when septics are functioning properly, they do not remove nitrogen from waste flow so it eventually seeps into ground and surface waters. Encourage your government to approve the installation of new septic technologies that will stop polluting our waterways.

  • Make your yard Ocean Friendly. Do not use chemical fertilizers and pesticides on your lawn. They pollute local waters with excess nutrients that cause toxic bloom conditions in coastal ponds and bays. By planting native plants, building healthy soils naturally, and shaping your garden to retain water and prevent runoff, you can help protect local water quality.

Efforts are even being made to take nuisance and harmful algae and make it into a useful product. For example, Bloomfoam is harvesting freshwater algae and making yoga mats and surf deck traction pads out of the final product. Now that’s both cutting down on the need for new petroleum-base products and helping to clean the water in affected areas. There are also efforts to convert algae into biofuel.

Resources : Fact Sheets & Case Studies

World Health Organization Guidelines for Safe Recreational Water Environments

Environmental Protection Agency Health and Ecological Effects

Environmental Protection Agency Cyanobacteria Fact Sheet

Environmental Protection Agency Guidelines and Recommendations

EPA - Partnering with States to Cut Nutrient Pollution

Center for Disease Control and Prevention Cyanobacteria

Sacramento-San Joaquin Delta

San Bernardino County

Sonoma County

Statewide Connecticut Department of Health

Statewide Department of Energy and Environmental Protection

NOAA - Red Tide Forecast

Surfrider Coastal Blog - A Brief History of Florida's Green Slime

Palm Beach County Chapter Algae Fact Sheet

Great Lakes
Great Lakes

Kansas River

Cheney Reservoir

Statewide Executive Office of Health and Human Services

Microcystis and Anabaena Fact Sheet

New Hampshire
Statewide Department of Environmental Services

Department of Environmental Services Fact Sheet

New Jersey
Statewide Ecological Impacts

Northern New Jersey

New York
Statewide Department of Environmental Conservation

Eastern Long Island Chapter Algae Fact Sheet

North Carolina
Statewide NOAA

Klamath Region


Statewide Department of Health

Statewide Department of Health

Statewide Current Lake Conditions

Statewide Department of Health

Olympic Region