&EPA
United States
Environmental Protection
Agency
Co-Branding
(optional)
HARMFUL ALGAL BLOOMS
AND DRINKING WATER
Co-Branding
(optional)
v>EPA
United States
Environmental Protect
Agency
PREVENTING HABS	MORE INFORMATION
Keeping the lakes and rivers that supply our
drinking water clean is key to ensuring clean
drinking water. Reducing the amount of nutrients,
such as nitrogen and phosphorus, in drinking
water sources can decrease the risk of HABs
and associated cyanotoxins impacting drinking
water. These excess nutrients typically originate
from agricultural, industrial and urban sources as
well as from atmospheric deposition. Lowering
this nutrient pollution will help keep drinking water
clean and can generally improve local water
quality (see Figure 2).
For more information about how HABs
are managed in your tap water contact your
public water system.
For more general information see
www.epa.gov/cyanohabs.
For more information about HAB-associated
illnesses, see www.cdc.gov/habs.
EPA: 810-F-16-005

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10-DAY HEALTH ADVISORIES LEVEL
SUMMARY
Freshwater harmful algal blooms (HABs) are
a growing concern in the United States and
worldwide (see Figure 1). Negative impacts
from HABs on water quality, human and animal
health and the economy can be significant.
Some HABs can produce toxins that are harmful
to humans and animals. These toxins can pose
challenges to drinking water supplies. Given this
risk, many drinking water systems are taking
actions to manage cyanotoxins in drinking water
and notify the public if levels become a public
health concern. Reducing nutrient pollution,
such as excess nitrogen and phosphorus, in
drinking water sources is important for the long-
term management of the risks HABs pose to
public health and water quality.
BACKGROUND
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).
Some HABs are capable of producing toxins,
called cyanotoxins, which can pose health
risks to humans and animals. Conventional
water treatment (consisting of coagulation,
sedimentation, filtration and chlorination) can
generally remove cyanobacterial cells and low
levels of toxins. However, water systems may
face challenges in providing drinking water during
a severe bloom event when there are high levels
of cyanobacteria and cyanotoxins in drinking
water sources. If cyanotoxins occur in tap water
over a 10-day time period at levels above the
national drinking water Health Advisories, people
are at risk of various adverse health effects
including upset stomach, vomiting and diarrhea
as well as liver and kidney damage.
ADDRESSING HABS IN DRINKING
WATER
The U.S. Environmental Protection Agency (U.S.
EPA) published national drinking water Health
Advisories for the cyanotoxins microcystins and
cylindrospermopsin (see Table 1). The Health
Microcystins

Children pre-schooi 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
Advisories provide the cyanotoxins levels at and
under which negative human health impacts
are unlikely over a 10-day period of time. Health
Advisories are developed to help states and
water systems assess local situations and
during emergency situations and spills. They are
not a federally enforceable, regulatory limit.
Given the health concerns that can occur from
cyanotoxins in drinking water, many water
systems are taking actions to manage and
reduce the risks from cyanotoxin contamination
in drinking water. These actions can include
steps for monitoring for cyanotoxins, adjusting
treatment to address contamination before
levels are of concern and notifying the public
through a Drinking Water Advisory when tap
water toxin levels are a possible public health
concern.

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