Are blue-green algae toxic and a health risk to humans?
Species of blue-green algae can include both
toxin-producing and non-toxin-producing strains, but there
are many species of blue-green algae that do not produce
toxins. Little is known about the environmental conditions
that trigger toxin production, and there is no way to tell
just by looking at a bloom whether or not it will produce
toxins. Over time, these toxins are diluted and eventually
break down and disappear.
Information regarding toxins from blue-green algae and
risks to humans, fish and wildlife is very limited, but the
cyanotoxins produced by the blue-green algae can be a threat
to fish, pets, livestock, wild animals and humans if
untreated surface water is ingested. There is no known
risk from eating fillets (muscle tissue) of healthy fish
caught in bloom-affected waters.
Currently, there are no state water quality guidelines for
recreational waters related to blue-green algae. However, it
is recommended that people do not swim in areas experiencing
How can humans be affected by blue-green algae toxins?
Blue-green algae can produce a number of toxins
that can affect the liver, digestive system and nervous
system, Most problems happen when water containing high
levels of toxin is ingested. Abdominal cramps, nausea,
diarrhea, and vomiting may occur if untreated water is
swallowed. Rashes can happen when skin is exposed to the
algae when swimming.
How can I prevent exposure to these toxins?
Most people avoid a blue-green algae bloom because they
tend to be icky-looking and smelly. It is important that people
and pets do not engage in recreational water activities in
blue-green algae blooms. It is especially important that
individuals and pets do not consume untreated surface water from
areas experiencing blooms. Boiling water does not remove or
destroy these toxins.
Ways to Limit Your Contact
with Blue-green Algae Toxins
- Do not drink, cook or shower with
untreated water from lakes, ponds or streams,
because there are many types of harmful bacteria
and other pathogens in the water bodies in
- Do not allow pets or livestock to swim in or drink scummy water. People should also not swim in water with the blooms.
- If you or your animals accidentally get into a blue-green algae bloom,
wash with fresh water and soap after skin contact, and avoid swallowing or inhaling water. Be sure to rinse all swimming suits and other wet clothing well as the bloom can become trapped in the material. Wash animals' fur thoroughly before they start to groom themselves.
- Avoid exposure to irrigation water drawn
from untreated sources.
- Notify your local water quality officials if you notice unusual changes in the taste or smell of your tap water.
Can blue-green algae supplements (such as Spirulina) contain
Some manufacturers collect their blue-green algae from
the wild where many types (toxic and nontoxic) can grow
together. A recent study found most of the products tested
had low levels of blue-green algae toxin. The US FDA has
received complaints from consumers about nausea; diarrhea
and other symptoms after taking blue-green algae supplements
but these cases have not been confirmed as being caused by
At this time, people who choose to use these products should
exercise caution. Children, pregnant women and people with
impaired liver function should avoid these products until their
safety has been proven.
Are there any drinking water standards for these toxins?
There are currently no standards for blue-green algae toxin levels in drinking water in the US. Other countries and the World Health Organization have developed