It is important to know the health hazards associated with algae blooms and to evaluate water quality every time you head to the lake or river. Please look for and follow the recommended signage at beaches. As a general rule, do not swim in water where you cannot see your feet in knee-deep water or if water is discolored or scummy. Even if the water looks clear it's important to avoid swallowing the water while swimming, as surface water can contain other bacteria and parasites besides blue-green algae that could make you sick.
Here are some helpful resources and tips from the Wisconsin Department of Health Services:
About Blue-Green Algae
Blue-green algae are a normal part of Wisconsin rivers and lakes. Problems arise if nutrients in the water are elevated, causing them to grow to high numbers also known as a bloom. Blooms are most common during mid to late summer. Blue-green algae blooms can create toxins that may make both humans and pets sick after they swallow, breathe in, or have contact with the water. Symptoms in humans may include:
- Vomiting
- Diarrhea
- Headache
- Abdominal Pain
- Cough
- Sore Throat
- Skin Rash Blistering
Blue-green algae poisoning in animals shares similar symptoms with heat stroke and water intoxication. Symptoms in animals may include:
- Vomiting
- Diarrhea
- Lethargy
- Loss of Coordination
- Seizures
If you or your pet develop an illness you think might be related to blue-green algae, talk to your healthcare provider or veterinarian and notify the Wisconsin Division of Public Health by filling out their online survey.
How to Keep You and Your Pets Safe
Here are some tips to stay safe when swimming:
- Avoid swimming in water that:
- Looks green like pea soup
- Has floating scum, mats, or films
- Has green dots or globs floating beneath the surface
- Has the appearance of spilled paint (green, blue, white, red, or brown)
- Always choose the clearest water you can find, especially when small children and dogs are swimming
- Do not swallow lake or river water
- After swimming, wash yourself and your pets with clean water
Note: Filamentous green algae that are long and stringy, like green hair, are not dangerous.
Why are we seeing blue-green algae blooms in the St. Croix River?
- Blue-green algae blooms are seen during periods of calm weather when wind speeds are low and waves are not strong. These conditions allow blue-green algae to float to the surface and form scums.
- Wind can push floating blue-green algae to the downwind shore, and with winds predominantly from the west during the summer, we may be seeing more of these accumulations on the east bank of the river.
- Blue-green algae are in all water bodies in Wisconsin. Waters with high nutrient levels are more susceptible, but even high-quality waters may experience surface blooms during periods of calm weather.
- Bloom monitoring is challenging because wind, waves, and river flow can change blue-green concentrations very rapidly. The best thing you can do to keep yourself and your family safe is to learn what blue-green algae looks like and to assess water conditions for yourself before swimming.
More Information
For more information on blue-green algae visit the Wisconsin Department of Health Services website and the Wisconsin Department of Natural Resources website.