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Since 2001, at least nine dogs have died after swimming in Mendocino and Humboldt counties’ rivers or brackish waters. In the summer of 2002, two dogs went into seizures shortly after emerging from the South Fork of the Eel River. Both died within fifteen minutes. Stomach contents revealed the presence of a deadly neurotoxin: anatoxin-a.

The dogs joined a grim list of wildlife, livestock, pets, and humans poisoned by blue-green algae, or cyanobacteria.
That green slime is nothing new—it evolved some 3 billion years ago, during the Archaean era, the first organism to produce oxygen as a waste product. What is new is that in response to dryer, warmer conditions, some of those algae species—especially the few toxic varieties—are proliferating in inland waterways. Scientists, public health officials, and water managers are worried that climate change may amplify a growing problem in California.

“With climate change, with hot, still conditions, the water supply sets up as big incubator cookers,” says State University of New York biochemist Grey Boyer. Boyer considers Northern California at high risk for the varieties of algae that manufacture a toxin. Algae enjoy conditions that describe us to a T: heavy winter rains that wash high-nitrogen fertilizers into creeks and rivers, followed by long, dry summers that dry up those creeks and rivers into quiet, isolated pools and shallows. As global climate change takes hold, some scientists believe toxic events may occur more frequently, and over a longer span of months.

Biochemist Boyer has worked with toxic algae species for forty years; he started out investigating marine red tides, a similar phenomenon but a different species of algae. The blue-green version, he says, comprises thousands of species, with only twenty or so capable of releasing toxins. The general consensus of algae experts, Boyer says, is that while blue-green algae as a whole will love the warming trends of climate change, the conditions are even more likely to favor the poisonous crowd.

The first recorded cases of human illness from cyanobacteria toxins occurred in 1931, along the Ohio River. According to Ian R. Falconer, in his book, Cyanobacterial Toxins of Drinking Water Supplies, the previous year had very little rainfall, and a tributary of the Ohio developed a heavy algal bloom. When rain finally came, that water moved into the Ohio and began making its way downstream, sowing symptoms of vomiting and diarrhea as it went. The most serious case of poisoning involving people took place in 1993, when a newly flooded reservoir in Brazil developed an immense cyanobacterial bloom, and 88 people died.

According to the World Health Organization, health impacts from blue-green algae can be immediate or devilishly long-lasting. For example, one toxin causes liver damage; in 1998, 117 kidney patients in Caruaru, Brazil, developed liver disease, and 47 died, after dialysis with water later found to contain cyanobacterial toxins. People with already damaged livers, such as those with hepatitis or cirrhosis, or children with smaller body weights, are more at risk.

Cyanobacteria offers frustrating conundrums to public health officials. Few of the species are toxic, but it’d take a scientist with a microscope to determine if a specific piece of floating gunk is releasing neurotoxins or not. “It’s a challenging thing to properly warn the public,” says Humboldt County environmental health field inspector Harriet Hill. “We can’t monitor all the freshwater bodies of Humboldt County. All we can tell people is to avoid areas that have blooms of algae.” The county posts warning signs at beaches and at events such as Reggae on the River. She says that she now gets a hundred calls a season, “mostly asking if we’re monitoring this river or that site. People are quite aware that there’s a potential for dog illness.”

Potential is the right word. Blue-green algae is everywhere and nowhere. Says SUNY professor Boyer: “It’s found in every environment, from soil, to water, to melt ponds in Antarctica. It’s small and robust, and it also has the capability to photosynthesize. Some produce spores that travel in the air, some have resting states like seeds. Some can survive for decades if not centuries. It’s hard to get it not to spread.”

Yet it’s ephemeral by nature. ‘We’ve had a half-dozen or so dog fatalities in this area,” he says. “We go back a half-day after the dog dies, and we can’t find anything. The wind blows the blooms to shore. The dogs swim through the water, lick their fur, and give themselves a concentrated dose.” And while dogs have other sources of drinking water, wildlife may not. “The algae takes a couple weeks to set up a big bloom,” says Boyer. “Animals have little choice if it’s the only water: You drink it and die, or you don’t drink it and die.”

Unfortunately, cattle like the taste of the mats of scum left on the shoreline. Recently a range bull died close to a reservoir on the Klamath River, and the suspicion was that he’d been felled by neurotoxins. But it couldn’t be proven, as the bull’s cells were too decomposed to measure the toxin. Humboldt County’s Hill says that initially Fish & Game officials were skeptical that blue-green algae had caused the dog deaths at Big Lagoon because wildlife did not seem to be affected. But Hill and Boyer note that it’s hard to measure wildlife deaths: Sick animals may head back to dens to die or their bodies may be eaten, leaving no trace of the toxin’s effects.

Some local scientists are investigating if the blooms can be harmful to people who come into casual contact with them. California Department of Public Health research scientist Sandra McNeel works with toxins of many sorts—molds, mushrooms, and more. She remembers receiving a call from a public health nurse in a North Bay county, asking if there were tests to determine if a patient had been exposed to blue-green algae toxins. “Our office tends to receive calls that don’t have an organizational home,” McNeel explains, and says that her interest was piqued.

She and her group devised a still-unreleased study on recreational exposure in two reservoirs on the Klamath,
Irongate and Copco. “We wanted to know if the toxins produced by blue-green algae in water became air-borne, and whether people swimming, waterskiing, or boating might be exposed to toxins by the inhalation route,” McNeel says. The study looked at two populations—people doing water activities at Klamath, and people playing in the waters of Lake Shasta, which doesn’t have trouble with blue-green algae. Participants gave blood samples and a nasal swab before and after going out on the water. Results are expected sometime in October.

McNeel notes the difficulty of tracking the toxins: “Most of the toxins reside inside the algal cells as long as they’re alive. You can take samples at various times of day and get totally different readings. And some [algae] can vary their own buoyancy so they can rise during the day to take advantage of sunlight and then sink during the night. It makes it hard to characterize what’s happening, especially in large bodies of water like reservoirs.”

What is the likelihood that blue-green algae will be a future bane? On the plus side, there have been no dog deaths in Humboldt County since 2004, which Hill attributes to successful warnings. On the minus side are factors Northern California has in abundance: heavy winter rainfall, high-nitrogen fertilizer use near into rivers and streams, long, dry summers that can turn tumultuous winter water courses into still pools and ponds. With our hot, dry summers and increasing likelihood of drought, California is a high-risk area for algae of any sort, especially for the toxic species.

“As a scientist I get uncomfortable speculating,” says McNeel. “But there’s good support in the literature to say that as our years get dryer and hotter, as water levels decrease in rivers and reservoirs and the Delta, that lower water levels and increased water temperatures
provide a better environment for blue-green algae to bloom.” She explains that with longer hot seasons blooms may start in May rather than July, and extend later in the year. Toxic blooms could even impact drinking water in reservoirs, as they have in Australia; in 2007, Sydney lost half its drinking water to a large blue-green algae column. Boiling or chlorine cannot remove toxins. In the future, water sources such as reservoirs may need to be covered, as photosynthetic algae requires light to grow.

Boyer says it’s unclear why some species are toxic. “We do know that it’s not to produce toxins to affect humans or animals,” he says. “It may be that [the toxins are] internal regulatory compounds, to control ion balance or a response to salt stress.” Sea-level rise—another result of climate change—may improve conditions for toxic blue-green algae for several reasons: shallow water, fertilizer runoff, still conditions, brackish water. “There’s a concern that with global warming, the salt will increase [inland],” Boyer says. “There is some concern that more brackish water will select for more toxic species.”

That seems to be happening already in the Delta. “The Delta rarely had blooms until about five years ago,” Boyer says. “Now it’s fairly common.” He notes that it’s hard to pinpoint causes, though he believes it’s a combination of less flushing action from the Sacramento
River and more fertilizers washing into the Delta. It’s easy to picture how this could become worse: Many scientists expect climate change to exacerbate storms, which could cause periodic flooding and fertilizer load runoff. When the weather changes, shallower water and pools become perfect spots for blue-green algae growth.

One positive note: Apparently freshwater fish are unaffected by the toxins. “They ingest the toxins,” says Boyer, but “they get rid of it as fast they accumulate. We’ve looked at thousands of fish samples. It’s hard to find toxins in fish.” But fish are not off the hook: “What usually happens,” Boyer says, “is that the algae grows and then dies, the decomposing bacteria uses up the oxygen [in the water], and the fish can die from low oxygen.”

So far, blue-green algae flies under most people’s worry radars, but that may change if the blooms find their way into city water supplies, and if creeks and rivers become danger zones. Hill points out that although algae can adapt to the likely conditions of global warming, it will not be so hospitable to nearly any other form of life. “Here’s something that can fix nitrogen from the air,” she says. “It’s got some traits of bacteria and some of algae, and it’s thought to be the first form of life. Imagine, the very species that produces our oxygen may be the last species left.”