By the time Tanya Bachman noticed something was wrong with her border collie, Jax, it was too late.
She and her family had taken their boat and two dogs out on the Columbia River near Portland, Oregon, in August 2024 to celebrate her birthday, a summer ritual as important to them as fireworks on the Fourth of July. That afternoon, Bachman let the dogs loose on an island beach to play. When Jax returned, his tail drooped.
As Bachman tried to attach Jax’s leash, he vomited, began convulsing and then lost consciousness. Bachman screamed for her husband, and the couple raced the dog to a veterinarian. It was no use; less than an hour after Bachman noticed Jax’s droopy tail, he was dead.
“It was just so shocking,” she said.
The veterinarian told them that Jax had likely ingested a toxic, algae-like microorganism called cyanobacteria, or blue-green algae, from a benthic bloom, a phenomenon scientists began documenting in the West about five years ago. Benthic blooms, which resemble globs of snot, form on stream bottoms or submerged logs or rocks, sometimes breaking free and rising to the surface. They are less familiar to Westerners than planktonic blooms, which form on the surface of lakes and reservoirs and look more like floating grass clippings or spilled green paint.
The cyanobacteria that cause planktonic and benthic blooms have existed in Earth’s waters for billions of years. Excess nitrogen and phosphorus from agricultural fertilizers or air pollution can cause them to proliferate. Research suggests that climate change is also contributing to more frequent and widespread blooms as warmer water stagnates during hot, dry years like this one, said Hannah Bonner, a professor and water scientist at Brigham Young University who studies benthic cyanobacteria.
It’s a cruel twist: As the West warms, once-inviting cool-water refuges may become a threat not just to pets, but to people and wildlife.
Cyanobacteria in both benthic and planktonic blooms can secrete toxic chemicals that irritate human skin, or, if consumed, cause nausea or even liver damage. The same toxins can kill any pets, livestock and wildlife that drink the contaminated water or lick their wet fur. No backpacking water–filtration systems can remove cyanobacteria toxins.
Most Western states only began tracking planktonic blooms — which are easier to spot and monitor than benthic blooms — in response to health concerns in Eastern waters. In 2014, toxic cyanobacteria blooms in Lake Erie shut down Toledo, Ohio’s drinking water system. Wyoming began monitoring blooms in 2018, first with satellite imagery and then, starting in 2021, with on-the-ground water sampling. Utah ramped up monitoring in 2016. California and Oregon’s programs, which are among the oldest in the West, started about 20 years ago.
Results from those and other programs suggest that planktonic blooms are popping up earlier in the season in more lakes and reservoirs and are lasting longer into the fall. Some experts believe the reported increases could be the result of more monitoring. But a nationwide Environmental Protection Agency study published in 2021 found that increased nutrients like nitrogen and phosphorus are combining with the warming and drying effects of climate change to create more and longer-lasting blooms.
“We’re affecting so much of the land surface and creating disturbances and introducing nutrients,” said Theodore Dreher, a microbiology professor emeritus at Oregon State University. Unlike climate change, where one continent’s emissions can affect the climate of another, nutrient pollution’s sources are often localized and can be more easily regulated. Utah, for example, has implemented regulations requiring improvements at places like wastewater treatment plants. It’s also created voluntary incentives for treating agricultural runoff and restoring floodplains. The combination has helped stem nutrient flow into Utah Lake, near Provo, where blooms were once so bad that people sold T-shirts with the slogan “Ski the Scum.”
In order to address the causes effectively, however, officials need to collect water quality data, not just monitor for blooms. Unfortunately, not enough are doing so, said Justin Hayes, Northern Rockies conservation director with American Rivers. “States need to take this really seriously and start trying to solve it rather than just warning people.”
“States need to take this really seriously and start trying to solve it rather than just warning people.”
Researchers are also still struggling to understand why recent blooms are turning up in unusual places. Planktonic blooms in high-elevation lakes far from septic systems and feedlots are becoming more common, possibly because of runoff from melting glaciers or atmospheric deposition of nitrogen and phosphorus from dust and air pollution, Bonner said. And benthic blooms may become more common as snowpack declines and produces less snowmelt. At the same time, parts of the West are seeing fewer monsoon rainstorms that can flush algal mats away.
“I was just in the mountains last weekend, in a pristine creek, and they were everywhere,” she said.
Bonner doesn’t think people should stay home to avoid blooms, but said they do need to know what to look for. A benthic bloom “is like a big ball of snot,” she said. “Find a stick, poke it, lift it up, and if you see hairlike strands or fibers, most of the time it’s not cyanobacteria or toxic. If it is a boogery consistency, it likely is.”
Meanwhile, more states are installing signs, sending email alerts, and posting public-health advisories that warn recreationists about toxic blooms.
And Bachman keeps talking to local and regional media, hoping Jax’s death will save someone else’s pet. “Everything upstream flows downstream,” Bachman said. “Just because you have a patch of it upstream doesn’t mean it won’t move down to you.”
Reporting for this story was supported by the Mighty Arrow Family Foundation.
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