Ecology

Blue-Green Algae

The common name for cyanobacteria, photosynthetic bacteria that form potentially toxic blooms in nutrient-rich lakes during warm weather.

What It Means for Your Lake

Blue-green algae is the widely used common name for cyanobacteria, a group of photosynthetic bacteria found in virtually every lake in Minnesota and Wisconsin. The name comes from the blue-green (cyan) color produced by the pigment phycocyanin, although blooms can also appear bright green, olive green, or reddish-brown depending on the species composition. In lakes, blue-green algae blooms typically appear as surface scums that look like spilled green paint, floating mats of greenish material, or a thick pea-soup consistency throughout the water column. These blooms form when water temperatures exceed 75 degrees Fahrenheit, phosphorus is abundant, and winds are calm enough for cyanobacteria to float to the surface using their gas vesicles. Blue-green algae blooms are most common in eutrophic and hypereutrophic lakes, but they can occur in any lake during unusually warm and calm periods. The Minnesota Pollution Control Agency reports that blue-green algae bloom reports have roughly doubled over the past 15 years across the state. Warning signs that a blue-green algae bloom may be present include water that looks like green paint has been poured in, a strong musty or earthy smell, dead fish along the shoreline, and pets becoming ill after swimming. If you suspect a blue-green algae bloom, avoid all contact with the water, keep pets and children away, and report the bloom to your state environmental agency. Many county public health departments now post warning signs at public accesses when blooms are confirmed.

Frequently Asked Questions