Copco and Iron Gate Reservoirs, which have created toxic conditions for the Klamath River’s fish for decades, are officially unsafe for humans to swim in this time of year.

The recreational health advisory “has become an annual ritual,” according to a news release from the Karuk Tribe Department of Natural Resources.

Copco and Iron Gate Reservoirs are currently at “danger” levels of toxic algae, according to the California Water Quality Monitoring Council’s Harmful Algal Bloom Incident Report Map.

The bloom is made up of tiny aquatic cyanobacteria called Microcystis aeruginosa, which secrete a carcinogenic liver toxin called microcystin. This is the same organism that blooms in Upper Klamath Lake following colonies of Aphanizomenon flos-aquae. Water with high concentrations of microcystin can be harmful or even fatal when ingested by humans and animals.

The release said even swimming in affected waters can result in eye irritation, rashes, mouth ulcers, vomiting, diarrhea and flu-like symptoms. In rare cases when people directly drank or inhaled the water, liver failure and nerve damage ensued.

Craig Tucker, resources consultant for the Karuk Tribe, said Microcystis was first observed in such concentrations in 2004, though PacifiCorp’s data and anecdotal observations suggested the blooms were happening (and even harming pets) since at least 2002.

Since then, the scum-filled reservoirs have become a yearly occurrence. Studies show that the concentration of microcystin in the water below Iron Gate Dam is still so high that it can negatively impact salmon hundreds of miles downstream.

The blooms have bad timing. They occur right as members of downstream tribes like the Yurok and Karuk use the ailing river for subsistence fishing. The Karuk hold ceremonies with specific timing rooted in centuries of tradition.

“They cannot be moved to another place or season when the water quality is safe,” the release said. “With blooms upstream, this puts tribal communities at a risk of exposure to the microcystin toxin.”

It’s also Labor Day Weekend. Water quality experts advise that vacationers shouldn’t recreate in the toxic reservoirs, which Tucker said look like antifreeze has been dumped into them.

“We know folks want to get outside and get one more weekend of summer in but we strongly urge everyone to avoid Iron Gate and Copco Reservoirs — they are a public health danger,” said Susan Fricke, Water Quality Program manager for the Karuk Tribe.

In California waterways, microcystin levels greater than 0.8 micrograms per liter trigger a “caution” level advisory for recreational use. Concentrations of 20 micrograms per liter or greater warrant a “danger” level.

This year, COVID-19 restrictions initially closed the EPA lab in Richmond, Calif., which analyzes the water quality samples. The Yurok and Karuk Tribes issued an emergency petition to reopen the laboratory earlier this summer, and it began accepting samples again — albeit with a much longer turnaround time due to staffing and operating limitations. Thus, the sampling has been slower than normal.

“It’s a challenging year for data,” Fricke said.

California first issued an advisory for Copco and Iron Gate Reservoirs on July 13, consistent with the yearly occurrence of microcystin in the water. Water samples taken in Copco Reservoir on August 4 showed concentrations as high as 290 micrograms per liter. Samples sent in just two weeks later showed 46,000 micrograms per liter — 2,300 times the danger level.

Though the upper basin is no stranger to Microcystis, water samples taken at the same time show relatively low concentrations of the toxin between the Link River and Copco Reservoir. In Keno and J.C. Boyle Reservoirs, the toxin was not detected. Fricke said that’s because the Microcystis in Copco and Iron Gate Reservoirs doesn’t come from the colonies in Upper Klamath Lake.“These blooms are developing themselves in the reservoirs,” she said.

A 2015 paper in the journal Harmful Algae found that Microcystin is far less common above Copco Reservoir, and that blooms in both Copco and Iron Gate Reservoirs are “internally generated.”

The analysis determined that the cyanobacteria in those reservoirs are genetically distinct from those in Upper Klamath Lake, and that their colonies persist nearly 200 miles from Iron Gate to the mouth of the Klamath River. This suggests that the reservoirs — not Upper Klamath Lake — are the main source of toxic algae on the Lower Klamath River.

Like Upper Klamath Lake, the reservoirs are stagnant pools of water that heat up significantly during the summer. The abundant warmth and sunlight, which gets layered in the water column, provides an ideal breeding ground for Microcystis. Add in nutrient-rich water flowing from hypereutrophic systems in the Upper Basin and the colonies take off.

Historically, algal blooms on the Klamath River didn’t used to get this bad. But dams impounding water and slowing down the natural flow of the river have given Microcystis the environment it needs to grow massive colonies.

The only solution, the tribe’s release said, is to remove the dams in accordance with the Klamath Hydroelectric Settlement Agreement.

It called on PacifiCorp parent company owner Warren Buffett to “keep the settlement on track” following an unexpected regulatory curveball from the Federal Energy Regulatory Commission in July.

“They’re big, warm, nutrient-rich bathtubs,” Fricke said. “The best measure is to turn them from a bathtub into a free-flowing river.”