When Good
Algae Go Bad

What You Can Do

Algae are an essential part of the
lake food web, but high levels of
nutrients like phosphorus
and nitrogen in our lakes
can contribute to large,
unsightly algal blooms.
Some algae species
(called blue-green
algae or cyanobacteria)
can produce toxins that
are harmful to pets, people,
and wildlife. EPA detected the
algal toxin microcystin in 39%
of lakes, but very rarely at
levels that represent
moderate or high
risk to the public.

Play it safe: keep people
and pets away from water
that is green, scummy
or smells bad. Report
algae blooms to
your local or state
health department
or environmental
agency. Learn
more at epa.gov/
nutrientpollution.

WARNING

KEEP OUT



How to Learn More

In the last 10 years, EPA and
its partners conducted two
large scientific studies of the
environmental conditions in
and around U.S. lakes. At EPA's
website for the National

Lakes Assessment,
you can view the
latest report,
explore the data,
and more. Visit:
epa.gov/national-
aquatic-resource-
surveys/nla.

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