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February 4, 2020

Emerald-green harmful algal blooms (HABs) have become an all-too-familiar summertime sight in many U.S. lakes and reservoirs. A new USGS study reports that the cyanobacteria that cause HABs also occur in large rivers.

Cyanobacteria were detected in 82% of the 50 samples collected from 11 large U.S. rivers, which span the country from the Willamette River in Oregon to the Chattahoochee River in Georgia. Cyanobacteria were detected at least once in each of those rivers. Although the cyanobacteria genes that indicate the potential for the cyanobacteria to produce toxins were present in all but one of the rivers, cyanotoxins themselves were found in just two of the rivers and in just 6% of the 50 samples.

The 11 rivers sampled were the Willamette, Sacramento, Mississippi, Connecticut, Delaware, Susquehanna, Missouri, Kansas, Ohio, Chattahoochee, and Trinity Rivers. The occurrence and concentrations of cyanotoxin genes were highest in the midcontinent rivers (Mississippi, Missouri, Kansas, Ohio, and Trinity Rivers).

Cyanobacteria and the cyanotoxins they produce are a global water-quality concern because of their potential to harm human and ecological health and cause economic damage. There has been an apparent increase in the frequency and severity of cyanobacteria-related events in recent decades, and cyanobacteria are expected to pose challenges to water quality well into the future.

Citation:  Jennifer L. Graham, Neil M. Dubrovsky, Guy M. Foster, Lindsey R. King, Keith A. Loftin, Barry H. Rosen & Erin A. Stelzer (2020) Cyanotoxin occurrence in large rivers of the United States, Inland Waters, DOI: 10.1080/20442041.2019.1700749

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