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Cyanotoxins are produced by cyanobacteria, formerly known as blue-green algae. While critical to water and soil in the environment, cyanobacteria that grow rapidly and excessively in lakes, reservoirs and other surface waters can produce toxic algal “blooms.” These algal blooms are most common during late summer and fall months and can appear as thick blue, green or brown mats on the water. Cyanobacteria can cause unpleasant tastes and odors in water even after it is cleaned at a treatment plant, and in some cases, cyanobacteria can produce potentially harmful cyanotoxins. In August of 2014, a toxin-producing algal bloom in Lake Erie prompted the water utility to issue a “do not drink” advisory to 500,000 Toledo residents.

People can be exposed to cyanotoxins in several ways:

  • ingesting fish or shellfish from waters containing cyanotoxins;
  • making skin contact with water containing cyanotoxins through showering or swimming or otherwise;
  • inhaling or ingesting toxins in the air when swimming or recreating in waters when cyanotoxins are present; or
  • consuming drinking water containing cyanotoxins.
Cyanobacteria blooms generally result from excess nutrient runoff into the drinking water supply, although there are other factors such as warmer water temperature that increase their growth as well. Nutrients, especially nitrogen and phosphorus, often are washed into rivers or other drinking water sources from agricultural operations and even from urban fertilizers.


The U.S. Environmental Protection Agency has identified cyanotoxins as a contaminants for possible future regulatory action. Depending on the type of cyanotoxin and the amount of exposure, health impacts from cyanotoxins in drinking water may include gastroenteritis and damage to the liver and kidneys. Swimming or recreating in waters with harmful algal blooms may lead to allergic reactions, including irritated eyes, ears and throat, gastrointestinal distress, and rashes and skin lesions. According to EPA, children under six may be at higher risk than the general population from at least two cyanotoxins, microcystins and cylindrospermopsin. EPA also advises that certain populations may be more susceptible than the general population to the health effects of these cyanotoxins, including nursing mothers and pregnant women, the elderly, and immune-compromised individuals or those receiving dialysis treatment.

The best way to know if cyanotoxins are a concern in your source water or treated drinking water is to contact your water utility or state public health agency. Depending on the source of your water, climate, and potential for nutrient pollution, your utility may or may not monitor for cyanotoxins. For example, if your water comes from groundwater sources, you water is less likely to be at risk from cyanotoxins.

As of early 2015, there are no federal regulatory standards or guidelines for cyanobacteria or cyanotoxins in drinking water. Several states, however, have requirements that utilities monitor for cyanotoxins and that consumers be notified when results show elevated levels in water in the distribution system. You can contact your water utility for details on how cyanotoxins are managed in your area.

The Safe Drinking Water Act (SDWA) requires EPA to publish a list of substances that could potentially be of concern and warrant further study, known as the Contaminant Candidate List (CCL). Cyanotoxins were listed on the third CCL as a group and were also included on the proposed CCL4. EPA’s evaluation is expected to focus on microcystins, and cylindrospermopsin.

In June 2015, EPA issued ten-day “health advisories” for microcystins and cylindrospermopsin. Health advisories indicate levels of contaminants in drinking water below which there are expected to be no health impacts. EPA has provided two different ten-day health advisory levels for each compound as shown below– one for children under six years old and another for children over six years old and adults.

  • Microcystins: 0.3 µg/L for children under six years old and 1.6 µg/L for children over six years old and adults
  • Cylindrospermopsin: 0.7 µg/L for children under six years old and 3.0 µg/L for children over six years old and adults
Researchers, regulators and utility managers will use these health advisories as they consider possible regulations and/or other management practices in the future.


Typically, groundwater wells are not expected to produce cyanotoxins. However, there could be exceptions if your well is directly affected by surface water.

If you get your drinking water from a private well, you should have your water tested by a certified laboratory regularly. Additional information about well water testing from EPA is available on their private drinking water well FAQ page.

If you are concerned about cyanotoxins in your drinking water, you may consider purchasing a home treatment device. However, in order to make a well-informed and cost-effective decision, consider:
  • Checking with your water system or consumer confidence report to learn about the amount of cyanotoxins in your water.
  • Identifying a device that has been independently certified to remove cyanotoxins.

NSF International, the Water Quality Association, Underwriters Laboratories and CSA International all certify home treatment products for removal of contaminants and to treat taste and odor problems. The relevant microcystin removal protocol is NSF Protocol 477. If you choose to use a home treatment device, it is very important to follow the manufacturer's operation and maintenance instructions carefully in order to make sure the device works properly.

Bottled water quality can vary. Bottled water in the United States is regulated by the U.S. Food and Drug Administration and is required to meet standards equal to the EPA’s tap water standards. There are also individual state standards. However, in most cases, you must contact the bottled water manufacturer for information about cyanotoxin levels.