Summer Scourge: Harmful Algal Blooms
My recent posts have highlighted good Great Lakes summer stuff: beautiful places, recreation, sand, sun. However, the summer months also bring an annual scourge to the lakes in the form of harmful algal blooms (HABs). The western basin of Lake Erie near Toledo is most affected by HABs, but increasingly the Green Bay of Lake Michigan and Saginaw Bay area of Lake Huron also experience them.
What are harmful algal blooms (HABs)? Algae are simple plants ranging in size from microscopic to large seaweeds. Harmful ones have a negative impact on their ecosystem, including animals and humans.
Why do they occur? HABs occur when harmful algae collect or merge together into clumps or masses that appear to grow or “bloom” if they expand in size. These blooms can be large. NOAAs forecast for Lake Erie as of August 5, 2025 has an algal bloom in the western basin of 160 square miles!
Conditions that develop toxic algae include shallow, warmer waters, hence the reason that Lake Erie and bay areas of other lakes are most susceptible. There are natural dynamics like wind and water flow that may bring algae together, but a lot of HABs are driven, or fed, by nutrients in the water. HABs are often exacerbated by an excess of nutrients (especially carbon, nitrogen and phosphorus) from lawns and farmland flowing in the watershed and in to the lake basins.
What is the impact of HABs? HABs can make animals or humans, or in some cases both, sick. For example, shellfish with traces of toxics can make a human consumer sick. People living near HABs can experience breathing issues, including exacerbated asthma, and eye irritation. HABs cause beaches and fishing and recreational areas to be closed causing economic loss to local economies.
How are they monitored? Lake Erie’s HABs are significant enough that they are monitored by the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Coastal Ocean Science. A variety of monitoring tools and data inputs are used with results compiled for key stakeholders and the public. Lake Erie HAB bulletins are issued at the start of July and posted twice a week through October or when the blooms have dissipated. See here for August 5, 2025’s bulletin.
These bulletins and associated information are critical to those in the water treatment sector, public agencies including health and agriculture, and the commercial and recreational fishing industry.
While there may be some debate about the preparation, there is no doubt that the existence of monitoring data was critical in August of 2014 when the city of Toledo had the unfortunate experience of a large algal bloom developing directly over its water intake unit in Lake Erie. This led to a “do not drink” advisory in the region that lasted over two days and affected a half-million people.
As I have written before, unfortunately, this drinking water crisis did not lead to the level of public, private and political action needed to significantly change agricultural practices and policies that could potentially alleviate some of the upstream causes of the HABs. But it did raise awareness and familiarity with HABs, shifting them in some people’s mind from simply a visual nuisance (that green gunk!) to an environmental issue.
What can be done about HABs? Earlier this summer, the Alliance for the Great Lakes released a statement about HABs (or toxic algal blooms as they are also called) stating the need to reconsider purely voluntary incentives in the agricultural sector regarding phosphorus reduction goals. Both Ohio and Michigan missed 2025 targets set in 2015. It will take a strong combination of voluntary action, policy and funding to change course. It seems unclear at this time whether key stakeholders will take action, leaving the potential for the blooms to be a new normal.
