Wet spring and rising temps lead to potential for harmful algae and need to reduce pollution

Nutrients in run-off 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 that 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.”

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.

Potential health impacts

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.

Tips to address the main cause of algae

Phosphorus, the top pollutant of concern in Minnesota lakes, fuels the growth of algae. In 25 percent of Minnesota lakes, levels of phosphorus and algae are too high, so the lakes don’t meet the water quality standard for recreation. Preventing phosphorus pollution is even more important in lakes warming as a result of climate change; warmer water also promotes algae growth.

An MPCA/Science Museum of Minnesota joint effort is helping solve a mystery about why periods of calm weather with little or no wind can result in algal blooms in Lake of the Woods that are so large they can be seen from space. While phosphorus and sediment levels are consistently high in the Red River Basin, there are exceptions. The Otter Tail River Watershed, which includes the cities of Fergus Falls, Pelican Rapids, Detroit Lakes, and Ottertail, stands out for generally good water quality and lower pollutant levels due to geography, significant amounts of undeveloped land, and actions taken by landowners and local partners. More than 3,500 projects in the watershed between 2004 and 2019 are helping to improve and protect water quality.

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.

How to report suspected harmful algal blooms

Email photos of suspected harmful algal blooms to algae.mpca@state.mn.us. For more information, visit the MPCA’s Blue-green algae and harmful algal blooms web page.