From Beachapedia

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 (see the Drinking Water Guide for more information), 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.”

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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.

There is increasing interest in considering the "One Health Approach" when addressing cyanobacteria effects. Here is an excerpt from the EPA explaining this approach:

A recent article by EPA researcher Elizabeth Hilborn and co-author Val Beasley of the University of Pennsylvania, "One Health and Cyanobacteria in Freshwater Systems: Animal Illnesses and Deaths are Sentinel Events for Human Health Risks,” uses a One Health approach to demonstrate how animal illnesses and death can be used as sentinel events to warn of human health risks associated with harmful algal blooms. The researchers found that illness or death among livestock, fish, and other animals are all events that may indicate the presence of harmful cyanobacteria that may impact human health.

Economic Costs of Blooms

In addition to human and environment health problems, cyanobacteria blooms can be extremely costly, impacting drinking water supplies, outdoor recreation industries, and more. One analysis by the Environment Working Group (EWG) estimates that US communities have spent over $1 billion in the last 10 years due to cyanobacteria blooms. Costs were estimated by state, with Ohio spending the most at an estimated $815 million, mainly due to a severe bloom in 2014 that impacted Lake Erie, a key drinking water reservoir for the state.

Health Guidelines and Policies

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The Environmental Protection Agency (EPA) issued an advisory for the amount of cyanobacteria in drinking water, and after several years in development, the EPA released Recreational Water Quality Criteria or Swimming Advisories for Cyanotoxins in May 2019.

The EPA’s recommended [water quality criteria] identify the following concentrations of microcystins and cylindrospermopsin that would be protective of human health given a primary contact recreational exposure scenario: 8 µg/L for microcystins and 15 µg/L for cylindrospermopsin... Given that cyanobacterial blooms typically are seasonal events, recreational exposures are likely to be episodic, and may be short-term in nature. If adopted as a [water quality standard], for impairment assessment and listing purposes, the EPA recommends states and authorized tribes use 10-day assessment periods, not a rolling 10-day period, over the course of a recreation season to evaluate ambient water body condition and recreational use attainment.

Due to the risk associated with recreational exposure to cyanotoxins, the EPA developed these criteria recommendations under the Clean Water Act (Ambient Water Quality Criteria) to protect human health while swimming or participating in other recreational activities in and on the water. The EPA has also provided additional resources to help people stay safe and informed.

While EPA was in the process of developing their cyanotoxin guidelines, some states 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.

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Map of freshwater algae bloom reports (including toxic and non-toxic blooms) from 2010 to 2019. For an interactive version click here.


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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Our elected officials need to pay attention to this public health and economic crisis and take action to control the flow of pollution into the waterways and beaches that drive our coastal tourism economy. See below for actions local community members, cities, and states can do to stop future severe algae blooms:

Actions we can all take:

  • Scoop the Poop. Pick up your pet’s waste.
  • Wash your car over grass or gravel, not on the street. Better yet take it to a commercial car wash.
  • Maintain your cesspool or septic system through proper inspection practices and not pouring harsh chemicals down the drain.
  • Make your yard more Ocean Friendly:
    • Go organic. Stop using chemical fertilizers and pesticides.
    • Apply mulch and compost to build healthy living soil instead.
    • Plant native and climate-appropriate plants.
    • Direct rain gutters and downspouts into your landscaping to slow down and sponge up rain. Learn more here.
  • Show up at City Council and demand the actions below.

Local jurisdictional actions could include:

  • Conduct mandatory septic tank inspections.
  • Post beach closures and health advisories quickly and publicly.
  • Pass strong local fertilizer restrictions (see Manatee County for a good example).
  • Implement proactive programs to control stormwater pollution, such as Ocean Friendly Gardens.
  • Inspect and maintain sewage infrastructure.

Statewide actions could include:

  • Set and enforce stronger water quality standards and regulations.
  • Help local communities transition away from septic systems to sewers (even when septics are functioning properly, they do not remove nitrogen from waste flow so it eventually seeps into ground and surface waters).
  • Provide funding to local municipalities to inspect and maintain their sewage infrastructure.
  • Regulate and restrict fertilizer inputs from agriculture into freshwater areas.
  • Restore natural flow of water to the coast.

Efforts are even being made to take nuisance and harmful algae and make it into a useful product. For example, Bloomfoam is hoping to harvest freshwater algae from US waterways to make yoga mats and surf deck traction pads out of the final product. This effort could cut down on the need for new petroleum-base products and help to clean the water in affected areas. There are also efforts to convert algae into biofuel.

Resources : Fact Sheets & Case Studies

Understanding Algae Blooms
What are Algae Blooms and Why Are they Bad?

Bloomwatch National HAB Reporting App

Center for Disease Control and Prevention Cyanobacteria

Environmental Protection Agency Cyanobacteria Fact Sheet

Environmental Protection Agency Guidelines and Recommendations

Environmental Protection Agency Health and Ecological Effects

EPA - Partnering with States to Cut Nutrient Pollution

World Health Organization Guidelines for Safe Recreational Water Environments

SeaGrant- Harmful Algal Blooms Facts

California Cyanobacterial and Harmful Algal Bloom Network (CCHAB)

California HABMAP

Central Valley Harmful Algal Blooms

Cyanobacteria and Drinking Water in California

Sacramento-San Joaquin Delta

San Bernardino County

Sonoma County

SWAMP's California Freshwater HAB Assessment and Support Strategy

SWAMP HAB Field Guide

Do you suspect a local harmful algal bloom in California? Report it here

Connecticut Department of Health- Blue–Green Algae Blooms in Connecticut Lakes and Ponds Fact Sheet

Statewide Department of Energy and Environmental Protection

Department of Natural Resources- Blue-Green Algae in Delaware

Florida Health- Harmful Algae Blooms

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 Environmental Research Laboratory

Indiana Department of Natural Resources- Swimming, Boating and Harmful Algal Blooms

Illinois Department of Public Health- Harmful Algal Blooms

Kansas River

Cheney Reservoir

Maine Department of Environmental Protection- Cyanobacteria

Department of Public Health- Harmful Algae Blooms

Statewide Executive Office of Health and Human Services

Microcystis and Anabaena Fact Sheet

Department of Health- HAB Fact Sheet

New Hampshire
Statewide Department of Environmental Services

Department of Environmental Services Fact Sheet

New Jersey
Department of Environmental Protection- Cyanobacterial HABs

Statewide Ecological Impacts

Northern New Jersey

New York
Statewide Department of Environmental Conservation- Harmful Algal Bloom Notification Page

Department of Environmental Conservation- Harmful Algal Blooms and Marine Biotoxins

Eastern Long Island Chapter Algae Fact Sheet

North Carolina
Statewide NOAA

Klamath Region


SeaGrant- Harmful Algal Bloom FAQ

Rhode Island
Department of Environmental Management- Harmful Algal Blooms

Statewide Department of Health

Statewide Department of Health

Statewide Current Lake Conditions

Statewide Department of Health

Olympic Region

Department of Health Services- Understanding Algae