Blue-green algae blooms: “when in doubt, keep out”

Image of Blue-Green Algae
Blue-green algae bloom_Photo by Barr Engineering

Blue-green algae blooms

“When in doubt, keep out”

Have you come across a lake that looks like it has spilled green paint on it or has a pea-soup appearance? If so, it is possible the lake has a blue-green algae bloom. Blue-green algae, also known as cyanobacteria, are a natural part of our freshwater systems, but these algae blooms can become harmful to people and pets. These blooms typically occur later in summer, but the recent hot weather adds to the possibility of earlier blooms.

During a blue-green algae bloom, the water may look like it has spilled green paint on the surface, but can also take on other appearances. Not all blue-green algae blooms are harmful. However, when conditions are right, these blooms can secrete toxins that are harmful to people and pets. Harmful algae blooms are most likely to occur during warm weather in shallow, nutrient-rich lakes. You and your pets can become sick if you have contact with, inhale airborne water, or swallow water that contains blue-green algal toxins. So, it is best to avoid contact with lakes with potential blue-green algae blooms. Always remember, when in doubt, best keep out.

2022 MPR article

What if I suspect a blue-green algae bloom?

In general, if you suspect a blue-green algae bloom contact the Minnesota Pollution Control Agency (MPCA) or the Minnesota Department of Health (MDH).

  • MPCA lake monitoring staff track reports of potential harmful algae blooms. You can email pictures of the suspected bloom to, call 651-757-2822 or 800-657-3864.
  • Report human health effects to the Minnesota Department of Health (MDH) Foodborne and Waterborne Illness Hotline at 1-877-366-3455. For health questions, citizens can contact MDH’s Waterborne Diseases Unit at 651-201-5414.

More Information

MN Pollution Control Agency’s Blue-green algae and harmful algal bloom page:

MN Department of Health’s Harmful Algal Bloom Fact Sheet: