Blue-Green Algae Toxicosis in Wisconsin Waters
If you think you are experiencing symptoms related to exposure to blue-green algae (e.g.,
stomach cramps, diarrhea, vomiting, headache, fever, muscle weakness, difficulty breathing),
contact your doctor or the Poison Information Hotline (800-222-1222) right away.
If your pet displays symptoms such as seizures, vomiting, or diarrhea after contact with surface
water, contact your veterinarian right away.
Report a Case with potential health effects caused by blue-green algae, visit the Department of
Health Services. or contact the Bureau of Environmental and Occupational Health at 608-266-
For more information about contacting your local health department, check the Department of
Health Services Web site.
If you are (or your local community is) interested in collecting samples for analysis, please
contact the Wisconsin State Laboratory of Hygiene at (800)442-4618. The Wisconsin Department
of Natural Resources is not currently conducting any routine monitoring for blue-green algae or
blue-green algal toxins.
• General Information
• Potential Effects on Humans and Animals
• Drinking Water Concerns
• Recreational Water Concerns
• Fish Consumption Concerns
• Measures People Can Take to Protect Themselves
• Measures People Can Take to Help Reduce Future Blue-Green Algae Blooms
• This information in PDF [PDF]
What are blue-green algae?
Blue-green algae, also known as Cyanobacteria, are a group of photosynthetic bacteria that many people refer to as “pond scum.” Blue-green algae are most often blue-green in color, but can also be blue, green, reddish-purple, or brown. Blue-green algae generally grow in lakes, ponds, and slow-moving streams when the water is warm and enriched with nutrients like phosphorus or nitrogen.
When environmental conditions are just right, blue-green algae can grow very quickly in number. Most species are buoyant and will float to the surface, where they form scum layers or floating mats. When this happens, we call this a “blue-green algae bloom.” In Wisconsin, blue-green algae blooms generally occur between mid-June and late September, although in rare instances, blooms have been observed in winter, even under the ice.
Many different species of blue-green algae occur in Wisconsin waters, but the most commonly detected include Anabaena sp., Aphanizomenon sp., Microcystis sp., and Planktothrix sp. It is not always the same species that blooms in a given waterbody, and the dominant species present can change over the course of the season.
How do blue-green algae differ from true algae?
What are the concerns associated with blue-green algae?
Blue-green algal toxins are naturally produced chemical compounds that sometimes are produced inside the cells of certain species of blue-green algae. These chemicals are not produced all of the time and there is no easy way to tell when blue-green algae are producing them and when they are not. When the cells are broken open, the toxins may be released. Sometimes this occurs when the cells die off naturally and they break open as they sink and decay in a lake or pond. Cells may also be broken open when the water is treated with chemicals meant to kill algae, and when cells are swallowed and mixed with digestive acids in the stomachs of people or animals. The only way to be sure if the toxins are present is to have water samples analyzed in a laboratory using sophisticated equipment.
Are blue-green algae blooms a new problem?
What is Cylindro and how is it different?
Why do blooms sometimes appear overnight?
Should I get treat a blue-green algae bloom with a chemical to get rid of it?
What can be done to reduce the frequency and intensity of blue-green algae blooms?
Regulatory agencies like the Wisconsin Departments of Natural Resources and Agriculture, Trade, and Consumer Protection are working with communities around the state to reduce stormwater runoff and to encourage agricultural practices that reduce soil erosion while maintaining high crop yields. Locally, landowners and interested citizens can help minimize the problems associated with algal blooms by working together with partners in their watersheds to reduce the amount of nutrients that reach nearby lakes, streams, and ponds. You can help reduce nutrient concentrations by promoting the following practices in your community:
- Prevent yard debris (e.g., leaves, grass clippings, etc.) from washing into storm drains
- Support local ordinances that require silt curtains for residential and commercial
- Plant and maintain vegetative buffer strips along shorelines of lakes, ponds, and streams. Note: Native plants are much more effective at filtering runoff than the typical grass species found on residential lawns.
Use lawn fertilizers only where truly needed
Has the Wisconsin Department of Natural Resources conducted any monitoring for blue-green algae?
Also, unlike the beach monitoring study for bacteria, this study was not designed to provide real-time information on the presence of blue-green algae or blue-green algal toxins, and only a limited number of surface waters could be monitored in each region of the state. However, when DNR received information from the State Laboratory of Hygiene on the presence of high counts of blue-green algae or on the presence of blue-green algal toxins, this information was shared with the local public health agency. Only the Department of Health and Family Services or the local public health agency has the authority to close a beach.
The total number of samples collected in the statewide monitoring study was 187 in 2004, and 194 in 2005. Blue-green algae were present in 74% of all samples collected in both 2004 and 2005 (again, samples were collected from sites where we believed the potential for blooms was high). Blooms occurred in all regions of the state, with the biggest “hot spots” in the west-central and south-central regions. Species of blue-green algae most commonly detected included Anabaena sp., Aphanizomenon sp., Microcystis sp., and Planktothrix sp. Alerts were sent out to local public health agencies when concentrations of blue-green algae likely exceeded the World Health Organization (WHO) guideline of 100,000 cells/mL. This concentration represents a “moderate risk to human health.” The total number of alerts sent out was 33 in 2004 and 42 in 2005.
A subset of the total number of samples collected was analyzed for toxins at the end of each summer (45 samples in 2004, and 34 samples in 2005). Microcystin-LR (a hepatotoxin) was the toxin detected most frequently and in the highest concentrations. This toxin was detected in the northern, south central, and west-central regions of the state. The toxin anatoxin-a (a neurotoxin) was detected in samples collected in the northern and south-central regions, and its presence was associated with a dog death in 2004. The toxin cylindrospermopsin was never detected.
Potential Effects on Humans and Animals
Can blue-green algae make me sick?
Dermatotoxins and Gastrointestinal Toxins: These toxins affect the skin and mucous membranes, and can cause allergy-type reactions such as rashes, eye/nose/throat irritation, and asthma, as well as headaches, fever, and gastroenteritis (nausea, stomach cramps, vomiting, diarrhea).
Examples include lyngbyatoxin and lipopolysaccharide endotoxins.
Hepatotoxins: These toxins affect the liver and other internal organs, and can cause gastroenteritis, tissue damage, muscle weakness, paralysis, and respiratory failure (with acute exposure), tumors, and possibly liver cancer (with long-term, chronic exposure). Examples include microcystins and nodularins.
Cytotoxins: These toxins also affect the liver and other organs (though through a different mode of action than hepatotoxins) and can cause malaise, headache, anorexia, vomiting, chromosome loss, DNA strand breakage, and damage to organs. An example is cylindrospermopsin.
Neurotoxins: These toxins affect the central nervous system and can cause seizures, paralysis, respiratory failure, or cardiac arrest. Examples include anatoxin-a and saxitoxin. (Saxitoxin is the same toxin associated with red tide and paralytic shellfish poisoning in marine systems).
Are children more vulnerable than adults?
- Children love to play in the water but typically do not understand the health risks as well as adults. As a result, they may drink the water because they are thirsty or swallow it accidentally while swimming.
- Children weigh less, and so a smaller quantity of toxin may trigger an adverse effect.
Can blue-green algae make my pet sick?
Should I let my pets or livestock drink or swim in water containing algal blooms?
Drinking Water Concerns
Can I be exposed to blue-green algae or blue-green algal toxins through my drinking water?
Exposure to blue-green algae or blue-green algal toxins is unlikely if your water is provided by a municipal drinking water agency. For most Wisconsin residents and tourists, drinking water is provided by underground water sources that do not contain blue-green algae or blue-green algal toxins. While Lake Michigan and Lake Superior serve as water supplies for many communities on or near those lakes, there is no reason to worry since the water is pumped from far offshore, in deep water areas that are not affected by blue-green algal blooms.
Rainbow Lake in Waupaca County and Lake Winnebago are the only two Wisconsin inland lakes that serve as water supplies for area communities (Appleton, Neenah, Menasha, and Oshkosh). While blue-green algae blooms may occur on these lakes in summer, studies have shown that blue-green algal toxins are removed by the local utilities’ routine water treatment processes.
Keep in mind that water that is not treated may pose risks far beyond those associated with blue-green algae. All natural surface waters contain bacteria, algae, viruses, and other pathogens that if consumed may post health risks to humans, pets, and other domestic animals. No one should ingest raw lake or pond water at any time.
How do water treatment plants deal with blue-green algae?
Can I treat my water at home to remove blue-green algae and their toxins?
Can I cook using water with blue-green algae in it?
No. Boiling water does not remove blue-green algal toxins. Because it is impossible to detect the presence of toxins in water by taste, odor, or appearance, you are better off assuming they may be present.
What about using water with blue-green algae for washing?
Recreational Water Concerns
Can water containing blue-green algae blooms be used for recreational activities?
Is it safe to let your children or pets swim in ponds (e.g., farm ponds, stormwater detention ponds, golf course ponds)?
By design, many farm ponds, golf course ponds, and stormwater detention ponds are constructed to trap nutrients, eroded soil, and other debris. By doing so, they prevent such materials from reaching nearby lakes, ponds, and streams. But because more nutrients may be available and because these types of ponds are generally more shallow and warm, it is possible for them to experience more frequent blue-green algae blooms (which may produce toxins). Again, a common sense approach is recommended for such ponds: if a scum layer or floating mat is present, do not let your children or pets swim.
Is there a risk to SCUBA divers who swim in blue-green algae blooms?
Do blue-green algae pose a risk to competitive swimmers such as triathletes?
When organizers establish the schedule and pick a course for a triathlon, they have no way of knowing whether or not a blue-green algae bloom will be present in the swim area. To the degree possible, race organizers are encouraged to establish a course that minimizes the exposure of participants to blue-green algae blooms. Race organizers may also want to consider having a rinse station established near the swimming finish area. All participants are encouraged to minimize the ingestion of water during the course of the event. As is the case in any organized race, participants should seek medical attention if they show any signs of illness during or after the event.
Fish Consumption Concerns
Can I eat fish from water containing blue-green algae?
Some blue-green algal toxins have been shown to accumulate in the tissues of fish and shellfish, particularly in the viscera (liver, kidney, etc.). Whether or not the accumulation levels are sufficient to pose a risk to humans is uncertain, although it would depend in part on the levels of consumption and on the severity of the blue-green algae blooms where the fish or shellfish were caught or collected.
The World Health Organization advises that people who choose to eat fish taken from the water where a blue-green algae bloom is present eat such fish in moderation and avoid eating the guts of the fish, where the accumulation of toxins may be greatest. Also, take care to not cut into organs when filleting the fish and rinse the fillets with clean water to remove any liquids from the guts or organs before freezing or cooking.
Important Note About Hygiene
Measures You Can Take to Protect Yourself
- Do not swim in water that looks like “pea soup”, green or blue paint, or that has a scum layer or puffy blobs floating on the surface
- Do not boat, water ski, etc. over such water (people can be exposed through inhalation)
- Do not let children play with scum layers, even from shore
- Do not let pets or livestock swim in, or drink, waters experiencing blue-green algae blooms
- Do not treat surface waters that are experiencing blue-green algae blooms with any herbicide or algaecide– toxins are released into the water when blue-green algae cells die
- Always take a shower after coming into contact with any surface water (whether or not a blue-green algae bloom appears to be present; surface waters may contain other species of potentially harmful bacteria and viruses)
Measures You Can Take to Help Reduce Future Blue-Green Algae Blooms
- Maintain native vegetation along shorelines as buffer areas
- Minimize activities that result in erosion
- Reduce the amount of fertilizer used on lawns
- Use only phosphorus-free fertilizer when possible
- Fix leaking septic systems
- Use only phosphorus-free detergents in dishwashing machines
If your pet displays symptoms such as seizures, vomiting, or diarrhea after contact with surface water, contact your veterinarian right away.
For more information about contacting your local health department, check the Department of Health Services Web site.
For more information on the potential health effects of blue-green algae, contact Dr. Mark Werner, Department of Health and Family Services, (608) 266-7480.
For more information on the ecology of blue-green algae or environmental factors that influence their growth, contact Jim Vennie, Department of Natural Resources, (608) 266-2212.
Last Revised: Thursday, August 06 2009