FREQUENTLY ASKED QUESTIONS
WHAT ARE HARMFUL ALGAL BLOOMS
AND CYANOTOXINS?
Cyanobacteria, formerly referred to as blue-green algae,
are found naturally in lakes, rivers, ponds and other surface
waters. When certain conditions exist, such as in warm
water containing an abundance of nutrients, they can rapidly
form harmful algal blooms (HABs). HABs can have negative
impacts on the ecosystem, human and animal health and on
the economy. Some HABs are capable of producing toxins,
called cyanotoxins, which can harm humans and animals.
WHAT ARE HEALTH ADVISORIES?
The U.S. Environmental Protection Agency (U.S. EPA)
publishes Health Advisories for unregulated contaminants
to help states and water systems assess local situations
and during emergency situations and spills. They are not
a federally enforceable federal regulatory limit. The Health
Advisories provide the contaminant levels less than or equal
to which adverse human health impacts are unlikely to occur
over a certain time period. As new information becomes
available, the U.S. EPA may develop updated advisories.
HOW DO HARMFUL ALGAL BLOOMS
AFFECT DRINKING WATER QUALITY?
HABs producing cyanotoxins can occur in water used
as sources of drinking water. If not removed during
drinking water treatment, exposure to cyanotoxins in tap
water above certain levels could be harmful to humans.
Additionally, algal blooms can create taste and odor
problems in drinking water, such as an earthy and musty
smell, which are not cause for human health concern.
WHAT ARE THE HEALTH EFFECTS FROM
CYANOTOXINS?
Drinking water containing cyanotoxins at levels
exceeding the U.S. Environmental Protection Agency's
national drinking water Health Advisories can put you at risk
of various adverse health effects including upset stomach,
vomiting and diarrhea as well as liver and kidney damage.
Seek medical attention if you or your family members are
experiencing illness.
Data for Illnesses associated with exposure are being
collected nationally at the Centers for Disease Control
and Prevention (CDC). To report a cyanotoxin-associated
iliness for humans and animals, please contact your state
or local health department.
WHAT ARE THE HEALTH ADVISORIES
FOR CYANOTOXINS?
The U.S. Environmental Protection Agency issued 10-Day
Health Advisories for the cyanotoxins microcystins and
cylindrospermopsin (see Table 1). Two distinct Health
Advisories were developed for two population groups 1)
infants and children younger than six years old and 2) adults
and children six years and older. For more information please
see https://www.epa.gov/nutrient-policy-data/drinking-water-
health-advisory-documents. Health Advisories were developed
for a 10-day exposure based on the most current science.
10-DAY HEALTH ADVISORIES
LEVEL
Microcystins
Children pre-school age and younger
(under 6 years old)
0.3 pg/L
School-age children (6 years and older)
1.6 pg/L
Cylindrospermopsin
Children pre-school age and younger
(under 6 years old)
0.7 pg/L
School-age children (6 years and older)
3.0 pg/L
Table 1. U.S. EPA's National 10-Day Health Advisories
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Agency
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FREQUENTLY ASKED QUESTIONS
WHY ARE THERE DIFFERENT
HEALTH ADVISORIES FOR THE TWO
POPULATION GROUPS?
Two different Health Advisories were developed because
of the variations in body weight and drinking water intake
between the different age groups. Bottle-fed infants and
young children under the age of six have higher water
intake relative to body weight as compared to adults
and children six years and older. Therefore, the Health
Advisories are lower for younger children than for children
six years and older and adults. Additionally, other groups
of individuals may be more vulnerable to cyanotoxins
including: pregnant women, nursing mothers, those with
pre-existing liver conditions, those receiving dialysis
treatment, the elderly and other sensitive populations. As a
precautionary measure, the lower level Health Advisories
could also apply to these individuals.
WHY DO OLDER CHILDREN HAVE
DIFFERENT HEALTH ADVISORY LEVELS
THAN YOUNGER CHILDREN?
The Health Advisories are lower for younger children than
for older children because young children under the age of
six consume more water relative to their body weight when
compared to adults and older children. Therefore, younger
children are at an increased risk of adverse health impacts
of cyanotoxins at lower levels.
WHAT HAPPENS IF YOU EXCEED THE
HEALTH ADVISORY LEVEL? IF IT IS A 10-DAY
VALUE, WHAT HAPPENS IF YOU EXCEED
FOR A SMALLER NUMBER OF DAYS?
The Health Advisory levels for microcystins and
cylindrospermopsin are non-regulatory concentrations
of drinking water contaminants at which adverse health
effects are not anticipated to occur over a 10-day exposure
period. Because it is difficult to determine in advance
the duration of elevated algal toxin levels, the U.S.
Environmental Protection Agency (U.S. EPA) recommends
that water systems begin to take actions once the elevated
levels have been confirmed by additional samples.
Additionally, because of time needed to process sequential
analytical tests, it can take several days following
the detection of a bloom and/or cyanotoxins before

concentrations above the Health Advisories are confirmed
in finished water. Therefore, the U.S. EPA recommends
initiating the response activities as soon as practicable.
WHAT DO THE GREEN, YELLOW
AND RED ADVISORY LEVELS OF
CYANOTOXINS MEAN?
Using the the U.S. Environmental Protection Agency's
national Health Advisory levels for microcystins and
cylindrospermopsin as a guide, ranges of cyanotoxin levels
in drinking water can be shown with the following advisory
levels: green, y and red (see Figure 1). Green
corresponds to drinking water toxin levels where adverse
health impacts are unlikely to occur for everyone,
indicates drinking water toxin levels where the risk of
adverse health impacts is higher for infants, young children
under the age of six and other vulnerable populations
(including: pregnant women, nursing mothers, those
with pre-existing liver conditions, those receiving dialysis
treatment, the elderly and other sensitive populations). Red
indicates drinking water toxin levels above which the risk of
adverse health impacts is higher for everyone drinking the
water. Drinking water systems can elect to issue Drinking
Water Advisories using these categories as guides.
Drinking Water Health Advisories
ADVISORY LEVEL
ACTION
Cyanotoxins detected
in tap water at levels
of concern.
Cyanotoxins detected
in tap water at levels
of concern for young
children and vulnerable
populations.*
Cyanotoxins not
detected in tap water
at levels of concern.
0
"Vulnerable populations = infants, children under the age of six, pregnant
women, nursing mothers, those with pre-existing liver conditions, those
receiving dialysis treatment, the elderly and sensitive populations.
Figure 1. Drinking Water Health Advisories
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Agency
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FREQUENTLY ASKED QUESTIONS
WHICH ADVISORY LEVEL SHOULD
SENSITIVE POPULATIONS OR NURSING
MOTHERS FOLLOW?
Populations such as nursing mothers and pregnant
women, those with pre-existing liver conditions, those
receiving dialysis treatment, the elderly and other sensitive
populations may be at risk of experiencing adverse health
effects of cyanotoxins at lower levels. As a precautionary
measure, such vulnerable populations should consider
following the health advisories stated for infants and young
children under the age of six.
WHAT HAPPENS IF CYANOTOXINS
ARE SUSPECTED OR FOUND IN THE
DRINKING WATER?
You may receive a drinking water advisory from your
public water supply if cyanotoxins above Health Advisories
are found in your tap water. If a drinking water advisory
is issued, follow the recommendations described in the
advisory notification. If you are concerned about the
potential occurrence of cyanotoxins in drinking water
please contact your public water system.
CAN I BOIL MY WATER TO MAKE IT SAFE
TO DRINK?
No, boiling water will not remove cyanotoxins and may
increase toxin levels.
WHAT SHOULD I DO IF I CONSUME
WATER WITH CYANOTOXINS?
If you or your family members have consumed water
that may have contained cyanotoxins at levels above
the national Health Advisories and you are experiencing
cyanotoxin-related illnesses, contact your healthcare
provider for medical attention. Data for illnesses associated
with exposure are being collected nationally at the Centers
for Disease Control and Prevention (CDC). To report a
cyanotoxin-associated illness for humans and animals,
please contact your state or local health department.
IF A DRINKING WATER ADVISORY IS
ISSUED, IS THE TAP WATER SAFE FOR
OTHER USES OTHER THAN DRINKING?
Given the current scientific understanding, it is unlikely that
showering, bathing, washing hands, doing laundry, etc. in
tap water with cyanotoxin levels near or below the Health
Advisory will be harmful to human health.
However, infants and young children under the age of six
should be supervised while bathing and during other tap
water-related activities to prevent accidental ingestion of
water. You may also accidentally consume water that is
used to prepare or wash your food, make beverages or
make ice. If a drinking water advisory is issued, the U.S.
Environmental Protection Agency recommends using
alternative water sources for these activities as well as
using alternative water sources to make infant formula.
CAN DIALYSIS BE IMPACTED BY
CYANOTOXINS?
Drinking water with elevated cyanotoxins levels can be
harmful to humans if used in dialysis treatment. The U.S.
Environmental Protection Agency recommends dialysis
centers and those using in-home dialysis use an alternative
source of water if their current water source becomes
contaminated with elevated levels of cyanotoxins. Please
consult your local health department or physician.
ARE THERE IN-HOME DEVICES THAT
CONSUMERS CAN USE PROTECT
THEMSELVES FROM CYANOTOXINS IN
DRINKING WATER?
Third-party organizations are currently developing
certification standards for in-home devices and are
evaluating how reliably they can remove cyanotoxins
from drinking water. The NSF International has certified
some filters in their ability to reduce microcystin to below
the national Health Advisory levels. More information
about these treatment units and the contaminants they
can remove can be found at: http://www.nsf.org/Certified/
DWTU/.
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FREQUENTLY ASKED QUESTIONS
WHAT ABOUT ANIMALS EXPOSED TO
CYANOTOXINS THROUGH DRINKING
WATER?
Cyanotoxins can be harmful to animals if they drink tap
water contaminated with elevated levels of cyanotoxins.
Contact a veterinarian if animals show signs of illness.
WHAT IS MY PUBLIC WATER SYSTEM
DOING TO ADDRESS HARMFUL ALGAL
BLOOMS OR CYANOTOXINS?
Contact your water public water supply to find out what
they are doing to reduce the risks of harmful algal blooms
and/or cyanotoxins in your drinking water.
WHERE CAN I FIND MORE INFORMATION
ABOUT HARMFUL ALGAL BLOOMS AND
CYANOTOXINS?
For general information, please visit http://www.epa.gov/
cyanohabs or contact your public water system, state,
or local government. For information about harmful algal
bloom-associated illnesses, please visit http://www.cdc.
gov/habs.
WHAT CAN WE DO TO HELP PREVENT
CYANOTOXINS FROM OCCURRING IN MY
DRINKING WATER SOURCES?
Reducing nutrient pollution, such as excess nitrogen and
phosphorus, is essential to decreasing cyanotoxins in
drinking water sources. Excess nutrients may originate
from agricultural, industrial and urban sources as well
as from atmospheric deposition. Things you can do
to reduce nutrients in drinking water sources include:
using phosphate-free detergents, disposing of your pet
waste properly, applying fertilizers only when necessary
and at the recommended amount and volunteering in
local watershed protection efforts. Additional prevention
activities can be found at https://www.epa.gov/
nutrientpollution/what-you-can-do.
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United States
Environmental Protection
Agency
EPA: 810-F-16-008
Co-Branding (optional)

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