Algae vs. “harmful algae” – what’s the difference?

Not all algae are harmful. Algae are natural components of marine and fresh water ecosystems, and form the foundation of most aquatic food chains. The most commonly occurring groups of freshwater algae are diatoms, green algae, and blue-green algae, which are more correctly known as cyanobacteria.

What’s a “harmful algal bloom” (HAB)?

Algae are efficient at converting sunlight and nutrients into more algae. So when conditions are right – sunny days with lots of phosphorus and nitrogen in the water – algae can multiply very rapidly, causing algae “blooms.”  Often these blooms have the potential to harm humans or ecosystems in which case they are known as “harmful algal blooms” or HABs. Different types of HABs may have different impacts; some can block sunlight from underwater habitats and clog fish gills. When large algae blooms die off, their decomposition can consume much of the oxygen in the water, creating hypoxic “dead zones” where few species can survive. The economic impacts of HABs range from fish kills in valuable fisheries, to tourism cancellations due to smelly, unsightly blooms, to increased costs at drinking water treatment plants for reducing taste and odor problems or removing cyanotoxins (see below). Learn more.

What’s a “toxic algae” outbreak?

Blue-green algae or cyanobacteria possess characteristics of algae – they make chlorophyll-a and use sunlight as an energy source for growth, but have bacterial cells (prokaryotic) rather than algal cells (eukaryotic). They are found in both fresh and salt waters. Some freshwater cyanobacterial blooms can produce highly potent toxins known as cyanotoxins. These blooms are known as “cyano HABS” or toxic algae outbreaks. In Lake Erie, the primary species of cyanobacteria is Microcystis aeruginosa, which can secrete a toxin called microcystin. If ingested, this toxin can make humans and animals very sick, or even cause death. Dangerous levels of microcystin have resulted in several drinking water alerts in the western Lake Erie basin in recent years, including the Toledo outbreak which caused a three-day ban on consumption of municipal water. Learn more.

Share This