Ecology

Cyanobacteria

Photosynthetic bacteria (commonly called blue-green algae) that can form harmful blooms and produce toxins dangerous to humans and animals.

What It Means for Your Lake

Cyanobacteria are an ancient group of photosynthetic bacteria that are among the oldest life forms on Earth, dating back over 3 billion years. Despite being commonly called blue-green algae, they are technically bacteria, not true algae. In Minnesota and Wisconsin lakes, cyanobacteria are a natural part of the phytoplankton community, but they become problematic when they dominate the community and form dense blooms. Several characteristics give cyanobacteria a competitive advantage in nutrient-rich, warm lakes: many species can fix atmospheric nitrogen, giving them access to a nutrient supply unavailable to other algae; they contain gas vesicles that allow them to regulate buoyancy and position themselves at optimal light levels; and they thrive at water temperatures above 77 degrees Fahrenheit, which are increasingly common during Upper Midwest summers. The primary concern with cyanobacteria is toxin production. Common genera found in regional lakes include Microcystis (produces microcystins, liver toxins), Anabaena/Dolichospermum (produces both microcystins and anatoxins, nerve toxins), and Aphanizomenon (produces cylindrospermopsin and saxitoxin). Exposure to cyanotoxins through swimming, swallowing water, or inhaling spray can cause skin rashes, nausea, vomiting, diarrhea, and in severe cases, liver failure. Dogs are particularly vulnerable because they drink lake water and lick contaminated fur. The Minnesota Department of Health and Wisconsin DHS maintain monitoring programs and issue advisories when cyanotoxin levels exceed recreational guidelines.

Frequently Asked Questions