Willamette River Algae Bloom Not Toxic to Humans

The blooms get worse with high temperatures.

Most of the Willamette River that runs through Portland is now poisonous to dogs. Due to toxic algae blooms, local health officials are now warning Portlanders to keep their pets out of the Willamette River from Ross Island to the Sauvie Island Bridge, a 14-mile stretch that includes most of the city’s waterfront.

The blooms get worse with high temperatures. But even with this week’s heat wave, the Oregon Department of Environmental Quality says it’s unlikely the blooms will become dangerous enough that humans will have to stay out of the water too.

The Oregon Health Authority says some toxins produced by algae blooms become harmful to humans when they exceed eight parts per billion. Right now, the levels in the Willamette are about 1.8 parts per billion.

“Typically, the lower Willamette blooms don’t produce a lot of toxins,” says Lauren Wirtis, a spokeswoman for DEQ, which tests for harmful algae bloom levels. “But that doesn’t mean we’re not monitoring the situation closely.”