VIDEO: DEQ investigating green scum floating down Willamette on Election Day

PORTLAND, Ore. () — A chain of green scum was seen floating through Portland on Election Day.

The substance was spotted on the Willamette River between the Marquam and Hawthorne bridges Tuesday afternoon. Oregon Department of Environmental Quality spokesperson Susan Mills told KOIN 6 News that the agency is looking into the issue.

"I've contacted our lab and cyanobacteria team to find out more," Mills said.

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In 2023, a similar looking scum was spotted on the river in mid-October. That scum was determined to be an unspecified species of floating aquatic plant. Because floating aquatic plants are considered nontoxic, the Oregon Department of Environmental Quality did not conduct toxicology tests.

In 2023, heavy rain was thought to have dislodged the aquatic plants from sloughs located upriver. Tuesday's sighting was also preceded by days of heavy rain.

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It remains unclear if the current material floating down the river is an aquatic plant species, toxic cyanobacteria or something else. However, experts don't expect to find cyanobacteria in the river during this time of year.

"One of our Water Quality Lab scientists is going to the river tomorrow morning to check this out," Mills said. "However, it's unlikely to be a harmful cyanobacteria bloom, as the conditions are not right for this time of year."