A frothy, green layer of muck recently coated a mileslong stretch of water on the Lower Snake River in southeast Washington, and scientists have warned people and their pets to stay away
Satellite images show the west-flowing river changed color from blue to a deep green over a short span of days. County workers posted signs along the contaminated stretch of river alerting the public to stay away from popular recreation spots for swimming, fishing and boating between Wawawai Landing and Central Ferry State Park, making a roughly 30-mile stretch of the river south and east of Pullman temporarily hazardous for humans, pets and livestock.
Algal blooms typically last days to weeks before dying off naturally and disappearing. Blooms are more common in stagnant bodies of water, such as lakes. In rivers, blooms happen more near dams or natural blockades that disrupt the current.
Alex Fremier, an environmental science professor at Washington State University, said the bloom on the Lower Snake is “unusually large” for a river. “The Snake River at that section has a bunch of dams on it,” Fremier said. “At this time of year, it functions more as a reservoir than a river.”
Algal blooms can harm water ecosystems when they die, because decomposing blooms absorb oxygen from the water. Low dissolved oxygen levels in water can kill fish and other river-dwelling animals and plants.
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