microcystin
noun
mi·cro·cys·tin
ˌmī-krə-ˈsi-stin 
: any of various toxins that are produced by freshwater cyanobacteria (genus Microcystis, especially M. aeruginosa), have hepatotoxic effects in animals including humans, and may occur in large quantities and contaminate water supplies during algal blooms (see bloom entry 2 sense 1d)
… two water samples from a Toledo treatment plant tested positive for microcystin, a toxin possibly caused by an algae bloom in Lake Erie. Residents were told not to drink, or even boil, the water tainted with microcystin, which can cause nausea and impair liver function.—
Lauren Raab
Lauren RaabWhen cyanobacteria die, they release microcystin, and scientists have found that remaining cyanobacteria respond to the molecule by making more of their own.—Carl Zimmer
Carl ZimmerExamples of microcystin in a Sentence
Recent Examples on the Web
Tests revealed no microcystins, according to the state.
—Joe Marusak, Charlotte Observer, 20 June 2025
Levels of the toxin microcystin have been detected in Lake Erie weeks earlier than usual, according to the National Oceanic and Atmospheric Administration.
—Julia Jacobo, ABC News, 13 June 2025
Blue-green algae and cyanobacteria are a natural part of freshwater ecosystems and are not all toxic, but state scientists sampled the nearby bloom Aug. 1 and detected microcystin toxins harmful to humans and aquatic life.
—Dinah Voyles Pulver, USA TODAY, 9 Aug. 2024
As Outside previously reported, saxitoxin can lead to paralysis, and microcystin can damage the liver if ingested.
—Julia Ries, Outside Online, 9 Aug. 2024
Microcystis, which is the most common bloom forming genus of cyanobacteria, can form a layer of green scum in Lake Erie and releases a toxin called microcystin.
—Miriam Marini, Detroit Free Press, 31 July 2021
The city has spent more than a billion dollars to upgrade its stormwater system and water-treatment plant, including improvements to filter and eliminate microcystin and a buoy with special sensors that monitor the extent of algal blooms near the city’s water-intake pipe in Lake Erie.
—Tim Folger, National Geographic, 17 Nov. 2020
The ban continued today, as further testing revealed evidence of the toxin microcystin in a drinking water plant.
—Tom Yulsman, Discover Magazine, 4 Aug. 2014
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Joe Marusak, Charlotte Observer, 20 June 2025
Levels of the toxin microcystin have been detected in Lake Erie weeks earlier than usual, according to the National Oceanic and Atmospheric Administration.
—Julia Jacobo, ABC News, 13 June 2025
Blue-green algae and cyanobacteria are a natural part of freshwater ecosystems and are not all toxic, but state scientists sampled the nearby bloom Aug. 1 and detected microcystin toxins harmful to humans and aquatic life.
—Dinah Voyles Pulver, USA TODAY, 9 Aug. 2024
As Outside previously reported, saxitoxin can lead to paralysis, and microcystin can damage the liver if ingested.
—Julia Ries, Outside Online, 9 Aug. 2024
Microcystis, which is the most common bloom forming genus of cyanobacteria, can form a layer of green scum in Lake Erie and releases a toxin called microcystin.
—Miriam Marini, Detroit Free Press, 31 July 2021
The city has spent more than a billion dollars to upgrade its stormwater system and water-treatment plant, including improvements to filter and eliminate microcystin and a buoy with special sensors that monitor the extent of algal blooms near the city’s water-intake pipe in Lake Erie.
—Tim Folger, National Geographic, 17 Nov. 2020
The ban continued today, as further testing revealed evidence of the toxin microcystin in a drinking water plant.
—Tom Yulsman, Discover Magazine, 4 Aug. 2014
Cite this Entry
“Microcystin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/microcystin. Accessed 30 Oct. 2025.
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