Toxic Algae Blooms

Toxic algae blooms put drinking water, pets and wildlife at risk. Let's stop the pollution fueling this green slime.

Toxic algae threatens our health, pets and wildlife
Aidan Banerjee

Summer Clean Water Intern, Environment America Research & Policy Center

What are toxic algae blooms?

In freshwater, toxic algae is actually bacteria (called cyanobacteria) that release toxins harmful to humans, pets and wildlife. Toxic algae blooms are fueled by excessive phosphorus or nitrogen flowing into our waterways, especially during warm weather.

Cyanobacteria outbreaks are sometimes referred to as harmful algal blooms (HABs) because they look like algae. However, HABs can also include excessive growth of non-toxic algae that deprive fish and wildlife of oxygen in the water. Cyanobacteria is also distinct from red tide, which occurs in marine waters.

How harmful are cyanotoxins?

Toxic algae can make us sick. Health effects range from skin rashes and headaches to vomiting, bloody diarrhea and pneumonia, according to the Environmental Protection Agency (EPA). One strain of cyanotoxins is listed as a chemical weapons agent. While toxic algae is only fatal to humans in rare instances, pets and other animals can get very sick and even die within hours of exposure to cyanobacteria.

In 2021, 16 states reported 117 human and 2,715 animal illnesses from toxic algae to the Center for Disease Control (CDC), with 90% of those cases from freshwater outbreaks. While these illness numbers do not include data from Florida, officials in the Sunshine state have issued more than 3,600 public health notifications on harmful algae outbreaks since July 2019.

Children are especially at risk from toxic algae because of their lower body weight, behavior, and toxic effects on development.

16 states reported illnesses from toxic algae to the CDC in 2021

How widespread are hazardous algae outbreaks?

Cyanobacteria events have occurred in all 50 states, according to the U.S. National Office of Harmful Algae Blooms. Moreover, the number of toxic algae outbreaks reported to the EPA increased each year from 2015 to 2023.

What causes toxic algal outbreaks?

Toxic algae outbreaks are caused by excessive nitrogen and phosphorus flowing into our waterways. This is sometimes called “nutrient pollution” because it makes cyanobacteria grow rapidly and produce toxins. Major sources of nutrient pollution into our waterways include:

Factory Farms

Industrial-scale livestock production – sometimes referred to as “Concentrated Animal Feeding Operations” (or CAFOs) – produce massive volumes of manure. All too often, the phosphorus and/or nitrogen from this animal waste winds up in our waterways – either as runoff when sprayed on farm fields or when heavy storms cause manure lagoons to overflow.  

Slaughterhouse Pollution

Meat and poultry processing plants have the highest levels of phosphorus and second highest levels of nitrogen in their wastewater when compared to other industries, according to the EPA. As many as 3,879 of these slaughterhouses and rendering plants release millions of pounds of pollution – either directly dumping it into our rivers or sending their untreated waste to sewage plants. Yet pollution limits on these  facilities have not been updated for at least 20 years, with standards for smaller operators dating back to 1975.

See our interactive map and fact sheet for more information on slaughterhouse pollution.

Staff | TPIN
A map of more than 300 slaughterhouse facilities.

Runoff and Sewage

Stormwater runoff, sewage overflows, and leaking septic systems contain significant nitrogen and/or phosphorus, the key drivers of toxic algae outbreaks. Impervious surfaces like roads and parking lots increase polluted runoff because stormwater can no longer be absorbed into the ground. Paving over wetlands and forests makes this problem even worse. From 1996 to 2016, U.S. coastal areas added 4.2 million acres of development, while losing 640,000 acres of wetland and almost 10 million acres of forest.

Algae-causing pollution is being made worse by climate change

Severe storms increase the flow of runoff from agriculture and sprawl into our waterways, and toxic algae grows more rapidly in warmer weather. So unless we dramatically cut the flow of phosphorus and nitrogen pollution into our waterways, toxic algae outbreaks are likely to become even more frequent and severe with climate change.

How to keep your family and pets safe from toxic algae?

Take the following precautions if you see green scum, foam or mats on a lake, pond or waterway:

  • Stay out of the water – including pets and livestock. 
  • Do not drink water or consume fish from waterways with toxic algae. Boiling water does not remove cyanotoxins.
  • Follow public health advisories and water use restrictions
  • Report potential outbreaks: Notify your local health department or environmental agency if you see signs of a potential outbreak. Officials can then test the water to confirm or rule out toxic algae.
Kids jumping into lake
Brocreative | Shutterstock.com

What are we doing to stop toxic algae?

Our rivers, lakes and ponds should be safe for swimming, fishing and as sources of drinking water.  We’re taking action to address  the root causes of toxic algae outbreaks:

Reducing slaughterhouse pollution:  Our organization is leading a broad coalition urging the EPA to issue a new rule that would reduce water pollution from meat and poultry plants by 300 million pounds per year – including major reductions in nitrogen and phosphorus.

Stemming the flow of manure from factory farms: Our researchers have documented the huge volume of manure generated by industrial livestock production. We are advocating for a moratorium on new or expanded factory farms, treatment of manure at existing CAFOs to prevent water pollution, and incentives for farmers to raise livestock on rotational pasture.

Holding polluters accountable: When companies contribute to toxic algae outbreaks, our partners at Environment America go to court under the Clean Water Act to stop their illegal pollution.

Repairing and improving water infrastructure: We are educating the public and decisionmakers about the need to repair our sewage and septic systems and invest in green infrastructure that absorbs stormwater and prevents runoff pollution. Congress did include some wastewater funding in the bipartisan infrastructure law, but the need is much greater – estimated at $630 billion or more over the next 20 years.

Protecting wetlands and forests: We are working at the state and federal levels to protect America’s remaining wetlands and forests, which help prevent toxic algae by absorbing stormwater and filtering out at least some pollutants that would otherwise flow downstream. 

Topics
Authors

John Rumpler

Clean Water Director and Senior Attorney, Environment America Research & Policy Center

John directs Environment America's efforts to protect our rivers, lakes, streams and drinking water. John’s areas of expertise include lead and other toxic threats to drinking water, factory farms and agribusiness pollution, algal blooms, fracking and the federal Clean Water Act. He previously worked as a staff attorney for Alternatives for Community & Environment and Tobacco Control Resource Center. John lives in Brookline, Massachusetts, with his family, where he enjoys cooking, running, playing tennis, chess and building sandcastles on the beach.

Aidan Banerjee

Summer Clean Water Intern, Environment America Research & Policy Center