Eclipse campers might be tempted to find an alternative source for drinking water in lakes or rivers, but the Oregon Health Authority is warning against that idea.

That’s because even a camper’s best efforts with water filtering and boiling won’t kill blue-green algae blooms that can cause diarrhea in humans and are potentially lethal for dogs.

“Any potential toxins that might be produced by a bloom that could be forming or could form on a water body cannot be reduced or eliminated in those ways,” said Rebecca Hillwig with the OHA. 

Officials have been warning of the potential for water shortages with an estimated 1 million eclipse visitors expected to flood into the state. The city of Bend has asked residents to eliminate unnecessary water use during the eclipse as a result.

But it’s also peak algae season in Oregon, and under the right conditions algae blooms can grow on just about any body of water.

The OHA says there aren’t cases of death by ingestion from the algae, but gastrointestinal symptoms, for which there are no antidote. Such symptoms can lead to dehydration, which can be lethal.

“They should be looking for water that’s foamy or scummy — definitely scummy,” Hillwig said. “It often looks like someone has thrown pea green or blue green paint into the water.”

If you’re unsure of whether or not you’re looking at algae blooms, Hillwig has this advice: “When in doubt, stay out.”