Are all blue-green algae dangerous?
There are many species of blue-green algae found in Wisconsin
lakes and rivers, but only certain species can produce the algal toxins
that cause illness. Not all algal
blooms produce toxin; a blue-green algae bloom may not
be producing toxins or producing enough toxin to cause a health concern.
Larger algal blooms have the potential for higher concentrations
of toxin. Unfortunately, there is
no immediate way to know if an algal bloom is dangerous or not.
It takes at least several days for a laboratory to analyze a
water sample to see if toxins are present. During that time, a harmless algal bloom may become more toxic, a
toxic algal bloom may become harmless, or the bloom could blow away or
dissipate all together. Algal
blooms can appear and disappear within hours, which makes it difficult
to decide when to close a beach. By
the time water quality analysis is done, water conditions may have
changed from the time a sample was collected. This is why it is so important to follow a common sense
approach. When you see an algal bloom, avoid the water and remember that
you should not allow your pets in water where an algal bloom is present! For
photos of algal blooms in Wisconsin see the
What are the common symptoms of algae-related illness?
Each algal toxin can affect your health
differently: neurotoxins affect your central nervous system, hepatotoxins
cause liver damage. Exposure to algal bloom material can also affect skin and
the gastrointestinal system. Symptoms depend on which toxin and how much of it you are exposed to, and
how you are exposed (drinking, swimming, etc.).
Common Human Symptoms:
Common Animal Symptoms:
Pets are especially susceptible to blue-green algae because they don't
naturally avoid smelly, green water. Because of their relatively small
size, animals do not need to ingest very much tainted water to become ill.
Many dogs have gotten sick and some have died as a result of drinking
water experiencing an algal bloom or licking their fur after swimming in
algae-filled waters. If you have a pet that enjoys swimming in the lakes
and rivers of Wisconsin, review our Pet-related
fact sheet (PDF, 39 KB) for more information about
keeping your animals safe from blue-green algae. Also, the Merck
Veterinary Manual (exit DHS) has additional information regarding algal
poisoning in domestic animals.
Please report algae-related illness to the
Wisconsin Harmful Algal Blooms Program.
PDF: The free Adobe Reader®
software is needed to view and print portable document format (PDF)