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Source: Minnesota Pollution Control Agency Although often referred to as algae, blue-green algae are not algae at all, but types of bacteria called cyanobacteria. Certain varieties of blue-green algae — shown here in Lake Crystal — can produce toxins that are linked to illness in humans and animals. Email pictures of the suspected bloom to

ST. PAUL — Nutrients in runoff from spring rainstorms combined with persistent hot weather on the way can mean trouble for lakes across Minnesota, triggering algal blooms that can be harmful to people and pets.

Recent reports of blooms already spotted across the state have led to swimming advisories. And with temperatures just now hitting the 90s and above, the Minnesota Pollution Control Agency (MPCA) predicts several more blooms could develop in time for the July 4 holiday weekend.

The MPCA advises people to stay out of lakes and streams if the water looks green and slimy, especially if it has a blue-green tint. The algae could contain toxic bacteria that can sicken people and kill dogs, livestock, and other animals within hours of contact.

Unfortunately, you can’t tell by looking at a bloom if it is harmful or not.

“If in doubt, stay out,” says Lee Engel, surface water monitoring supervisor for the MPCA. “Excess nutrients such as phosphorus and warm water temps are ideal for growing algae and causing nuisance blooms. Holiday weekends typically see more people out on Minnesota lakes to boat, fish, and swim, and due to this year’s conditions, we need everyone to remain vigilant in looking for potentially harmful algae, I added.”

“There are a lot of things people can do about algae, especially homeowners,” said Coalition for a Clean Minnesota Executive Director Scott Sparlin said. “People should look for phosphorus-free inputs and building soil health.”

Sparlin said some people have a tough time following fertilizer directions.

“Overapplication of fertilizer will cost you more, but may not get you more,” I have added.

Higher temperatures due to climate change have led to warmer lakes, too. The MPCA has documented increased reports of potentially harmful algal blooms in more places that persist throughout the season.

In recent years, multiple reports of dog deaths have been attributed to exposure to toxic algae. People can protect their dogs by:

• Keeping them out of algae-laden water

• Hosing them off immediately after playing in any lake or stream

• Preventing them from ingesting affected water or licking toxins from their coat

• Seeing a veterinarian immediately if your dog may have been exposed to blue-green algae

People who come into contact with toxic blue-green algae can experience skin, throat, eye, and nose irritation and nausea. If you come in contact with algae, rinse off with clean water afterward.

Phosphorus, the top pollutant of concern in Minnesota lakes fuels the growth of algae. In the Cannon River Watershed, 88 percent of the lakes studied don’t meet the water quality standard for recreation. While these lakes may be suitable for some recreation at times, efforts to reduce phosphorus need to continue and expand.

Reducing phosphorus pollution is even more important with lakes warming because of climate change; this means more days of open water and more opportunity for algae to grow.

Landowners and residents can help reduce phosphorus pollution in local lakes by:

• Reducing urban stormwater with rain gardens, rain barrels, and fewer impervious surfaces.

• Using phosphorus-free lawn fertilizer, keeping grass clippings and other yard waste out of storm drains, and picking up after pets.

• Building soil health to reduce cropland runoff by planting cover crops, increasing organic matter, and reducing tillage.

• Planting deep-rooted native plants along ditches, lakes, and streams to slow down and filter runoff.

• Managing manure responsibly to keep it out of lakes and streams.

• Maintaining a healthy septic system.

Email photos of suspected harmful algal blooms to algae at For more information, visit the MPCA’s blue green algae and harmful bloom web page.

(Fritz Busch can be emailed at

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