Blue-green algae: If in doubt, stay out

Contact: Risikat Adesaogun, 651-757-2056

St. Paul, Minn. — Temperatures are going up, and in Minnesota, many of us are cooling down at our favorite lakes. However, high temperatures combined with rainfall can create the conditions for harmful blue-green algae. This type of algae can harm pets, livestock and even people.

In late June, a child was hospitalized after being exposed to blue-green algae while swimming in Alexandria’s Lake Henry. Earlier in June, multiple dogs were sickened, and two dogs died from exposure to toxic blue-green algae in Red Rock Lake, located in Douglas County. While both of these instances occurred in the Alexandria area, blue-green algae blooms can impact lake waters throughout Minnesota.

The key to solving algae problems is to improve overall water quality by reducing how much phosphorus gets into lakes from urban and agricultural runoff and wastewater treatment systems.

What’s the risk?

The unpleasant odor and appearance of a blue-green algal bloom typically keeps most people out of the water. However, people can become sick after they swim, boat, waterski or bathe in water that has a toxic blue-green algal bloom. During these activities people are exposed to the toxins by swallowing, having skin contact with, or breathing in airborne droplets of water. If someone becomes sick, symptoms may include vomiting, diarrhea, rash, eye irritation, cough, sore throat and headache.

Dogs are at particular risk as they wade in shoreline areas where algae may accumulate. Dogs exposed to blue-green algae can experience symptoms such as vomiting, diarrhea, rash, difficulty breathing, general weakness, liver failure and seizures.

If you or your pets experience any of the above symptoms after visiting a lake, seek medical or veterinary assistance immediately.

Some safety tips for you

Not all blue-green algae are toxic, but there is no visual way to predict whether a blue-green algal bloom contains toxins and is harmful to humans or animals. Harmful blooms often look like pea soup, green paint or floating mats of scum, and sometimes have a bad odor. Blue-green algae may not look dense, and it doesn't always cover large areas of a lake. If algae is present in the water, toxic conditions can occur even without obvious signs of scum.

“If it looks and smells bad, don’t take a chance. We usually tell people, if in doubt, stay out,” said Pam Anderson, MPCA Water Quality Monitoring Supervisor. “If you’re not sure, it’s best for people and pets to stay out of the water.” Don’t swallow, swim or wade in water with blue-green algae. If you come into contact with blue-green algae, or if it gets on your skin, thoroughly wash it off, paying special attention to the swimsuit area. If you think your dog swam in water where blue-green algae were present, rinse them off with fresh water immediately.


There are currently no short-term solutions to fix a blue-green algal bloom. Once a bloom occurs, the only option is to wait for the weather to change — significant rainfall, wind shifts or cooler temperatures — to disrupt the algae’s growth. “With the intermittent periods of rain, followed by high temperatures, blue-green algal blooms will be common on many lakes throughout Minnesota for the remainder of this summer,” said Steve Heiskary, an MPCA Water Monitoring Research Scientist.

More information on blue-green algae, including information on reporting suspected human or animal cases, is available on the Minnesota Department of Health website.