Why Do I So Often See Clumps of Soapsuds in the Willamette River?

Why do I so often see clumps of soapsuds in the Willamette River? Maybe I’m old fashioned, but I thought soap only cleansed COVID off my hands. —Puzzled Along the Willamette Greenway

Our current historic moment seems to include a fetish for assuming that everything is deceitful, terrible or doomed. But is it? Jaded cynicism was all very well when it was confined to snarky culture critics (ahem) and the occasional private eye. Now that everyone from Lyft drivers to Herbalife reps feels qualified to declare all institutions corrupt, though, maybe it’s not so cool anymore.

Maybe it’s time to acknowledge that, every once in a while, the worst possible thing isn’t actually true. Take the sudsy Willamette: Those suds must be there because some evil multinational corporation bribed our Legislature into letting them dump surplus carcinogenic spermicide into the river, right?

For once, no. I’m as surprised as anyone! It’s true that pollution with detergents or foaming agents can lead to the production of suds like you’re seeing, Puzzled. In most cases, however, sudsing in rivers is the result of organic matter breaking down via normal biological processes.

“About 20 years ago, the Oregon Department of Environmental Quality did some water sampling to evaluate the Willamette’s foam and found it to be from natural diatoms,” says Travis Williams of Willamette Riverkeeper. Diatoms are single-celled plankton with shells made of silica, and when they die (usually at the ripe old age of a week or so), their shells break open, disgorging the contents into the surrounding water.

The diatom’s guts are rich in fatty compounds that act as surfactants (foaming agents) when agitated. To put it into almost comically Portland-friendly terms, they foam up in the same way that the oils in ground coffee foam up to form the crema on a shot of espresso. In the river’s case, however, the agitation is provided by Willamette Falls, which whips the diatomaceous lipids into long-lasting suds capable of making it from Oregon City to the Columbia and beyond.

In fact, Williams says, “the Willamette below the falls is a unique place to see large lines of foam.” Should he get out more? Maybe. But you can’t say he’s not looking at the bright side.

Questions? Send them to dr.know@wweek.com.