Greener Guidance Advice Column: Harmful Algal Blooms

Note: This is the second edition of NACCHO’s new Greener Guidance environmental health advice column. To learn more and submit a question for future editions, click here.

September 2018

Dear Greener Guidance,

One of our freshwater recreational lakes has had a harmful algal bloom (HAB) twice in as many years. What are your recommendations to address this? Why are we seeing more of these now? Is there anything lakeside communities can do to prevent HABs? What sort of routine monitoring should be done?

– Anne from Michigan

Dear Anne,

According to Dr. Tom Johengen, a research scientist with the Cooperative Institute for Great Lakes Research (CIGLR) at the University of Michigan, it is important to first find out what type of algae are associated with the bloom.

“There can be dense concentrations of non-toxic algae that are a nuisance to look at, but don’t really pose any health risks, or the bloom can be comprised of cyanobacteria that are known to produce toxins that could be harmful to pets and humans if at high enough levels.”

As far as what causes HABs, Dr. Johengen explained, “HABs are generally produced in ecosystems where there are excessive amounts of nutrient inputs. In big lakes the nutrients mostly come from tributary runoff. In smaller lakes it could be from lawn fertilizing or septic systems. Cyanobacterial HABs occur during warm conditions, and they are able to out complete other algae when water temperatures get above 20°C. So we tend to see them become dominant from mid-July through September.”

“The increase in frequency may be the result of more available nutrients or hotter temperatures,” said Dr. Johengen, “but another factor that might be contributing is that cyanobacteria form over-wintering cells (like wild flower seeds) and it provides an innocula for next years bloom. They do become self-perpetuating. Nutrient control is usually considered the main way to control the amount or extent of the bloom.”

Gary Kohlhepp, who works on surface water assessment at the Michigan Department of Environmental Quality (MDEQ), recommends reviewing this summary of cyanobacteria and associated algal toxins from LG sonic, as well as MDEQ’s webpage on HABs.

Reports of HABs can be submitted to, and MDEQ follows up on reports of harmful algal blooms by collecting samples and testing for microcystin (the most common algal toxin).

Mr. Kohlhepp also provided a list of additional lake water quality and management resources:

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