Cyanobacteria / Blue-Green Algae
Facts & Information

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Fact Sheets

What is a blue-green algae bloom?

A motor boat churns through the thick scum of a blue-green algae bloomBlue-green algae, or cyanobacteria, are an ancient group of algae. Although they are most closely related to other bacteria, they can photosynthesize like green plants. Blue-green algae reproduce rapidly in lakes and ponds with adequate amounts of sunlight, air/water temperature and nutrients like phosphorus and nitrogen.

Within a few days a clear lake or pond can become cloudy with algae growth. This is called a bloom. Although blue-green algae blooms can create nuisance conditions and undesirable water quality, most blooms are not toxic.

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Why be concerned about blue-green algae?

Some kinds of blue-green algae produce natural toxins or poisons. When these algae die and break down, toxins can be released into the water. Avoid contact with blooms and dense accumulations of these algae

Children are at higher risk of exposure to blue-green algae because they are more likely to drink the water.

Cyanobacterial toxins may cause illness

There are no documented cases in Vermont of human illness related to blue-green algae, however, caution around the algae is urged.

Depending on the type, amount and route of exposures, different types of health effects can be caused by cyanobacterial toxins.

A danger to pets

Do not allow pets in algae-contaminated water because they will also drink the water and consume algae on their fur.

If animals ingest the toxin, they can be quickly paralyzed and die. Signs of poisoning include weakness, staggering, difficulty breathing, convulsions and death. During the summer of 1999, the death of two dogs was attributed to blue-green algae poisoning after drinking large amounts of contaminated water directly from Lake Champlain.

If you believe that someone has become ill because of blue-green algae, seek medical attention and contact the Health Department at 1-800-439-8550.

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Signs of a toxic bloom may include


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How can I tell if blue-green algae is present in a bloom?

Blue-green algae blooms may look like:

When a blue-green algae bloom washes up on shore, it can form a thick mat or a foam on the beach.

Blue-green algae is made up of extremely small organisms that are hard to pick up and hold. In contrast, if you pick up algae and it is stringy, made up of long bright grass-green strands that feel either slimy or cottony, it is not blue-green algae, but harmless green algae.

Photos: What is and isn't a Blue-green Algae bloom

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If there is an algae bloom, when will it go away?

Generally, cooler weather, rainfall, and reduced sunshine will lead to the breakup of an algal bloom. Some blooms die off after a few weeks, while others persist for a few months, depending on the conditions.

Wind and waves can move algae around. Blooms can appear or disappear very rapidly, so conditions are likely to change over the course of several days.

Check the status of Blue-green Algae on Lake Champlain

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What if I see a bloom?

For much of the year, Lake Champlain is safe to swim in, but it is important to be aware of algae blooms. Blue-green algae blooms usually don’t happen until late summer and fall, but can happen earlier in a dry, hot year.

If the water is clear and the shoreline is free from green or brown scum, the water is probably safe to swim in. If there is a heavy greenish scum on the water or shore:

Laboratory tests of water samples can confirm whether or not a bloom is toxic.

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What can I do to help prevent blooms?

Algae blooms are likely to occur during sunny, calm weather when high concentrations of nutrients are present in water. The two important nutrients that can cause a bloom are phosphorus and nitrogen, found in animal and human waste and fertilizers.

To help decrease nutrients flowing into streams, ponds and lakes:

Learn more at Vermont Watershed Management Division

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Cyanobacteria and Neurological Diseases

Amyotrophic lateral sclerosis (ALS), sometimes called Lou Gehrig's disease, is devastating disease with no known cause. Only 5 to 10 percent of people with ALS have a family history (i.e. genetic cause) of the disease.

BMAA is an amino acid produced by some cyanobacteria (blue-green algae). Researchers are testing the hypothesis of a link between BMAA exposure and ALS. This research is very preliminary and has not been proven. The Health Department will continue to review information as it becomes available.

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