From the lake to the ocean, the waters of the Klamath are once again teeming with toxic blue-green algae at the end of a hot, dry summer.
Microcystis aeruginosa, a species of photosynthetic cyanobacteria that produces the neurotoxin microcystin, has been detected in nearly all reaches of the Klamath Basin at or below Upper Klamath Lake. The harmful algal blooms have plagued the basin and its residents for decades, fueled by nutrient runoff, stagnant water and summer sunshine.
Microcystin has negative health effects on humans when affected water is ingested, either through drinking or through inhaling spray from boats. Side effects include nausea, diarrhea and slurred speech. Dogs can be more seriously impacted, and some pets have died after exposure to Microcystis blooms in other water bodies. The public is urged to stay away from waterways with posted advisories, according to health officials in Oregon and California.
Copco Reservoir became 2021’s first bloom victim on July 21, after water samples collected there by PacifiCorp exhibited levels of microcystin at 30 parts per billion. Two weeks later, that concentration had jumped to 170 ppb. In California, the toxin is considered a public health danger at levels above 20 ppb.
The California Water Quality Monitoring Council issued a toxic algae “caution” advisory for both Copco and Iron Gate Reservoirs in mid-July, and expanded it to a “warning” after identifying visible bloom scum in the waters of both reservoirs.
Next came Upper Klamath Lake, which has reliably experienced a monoculture of cyanobacteria blooms since the mid-20th Century. The lake had been naturally eutrophic (rich in nutrients) and experienced algae blooms comprised of multiple species before colonization, but agricultural runoff and soil erosion in its tributaries and the loss of a majority of its water-filtering wetlands led to the takeover of two cyanobacteria species: Aphanizomenon flos-aquae and Microcystis. Microcystis feeds off the nitrogen left over by desiccated AFA blooms in early summer, causing water quality problems that ripple throughout the watershed.
The Oregon Health Authority issued a harmful algal bloom advisory for Eagle Ridge County Park, on the lake’s western shore, on July 30. It expanded that to Howard Bay a month later, and on September 10 issued an advisory for the entire lake based on a microcystin concentration of 910 ppb.
Oregon also issued an advisory for J.C. Boyle Reservoir on September 10, based on water samples containing 18 ppb of microcystin.
The algal blooms are having downriver impacts, too. Monitoring by the Karuk and Yurok Tribes have detected low concentrations of microcystin in sites from below Iron Gate Dam all the way to the Klamath River Estuary. California posted a “caution” level advisory for the river between Iron Gate and Weitchpec, and the Yurok Tribe issued one for Weitchpec through the river mouth.
In past years, algae throughout the system have persisted late into the fall and early winter depending on environmental conditions. An interactive map of updated toxic cyanobacteria advisories can be accessed through the Klamath Basin Monitoring Program.