Water samples taken from Copco and Iron Gate reservoirs contain extremely high levels of the toxic blue-green algae Microcystis aeruginosa for the third consecutive year since monitoring began in 2005, according to a news release from the Yurok Tribe.

Microcystis aeruginosa produces the toxin microcystin, which is known to cause liver failure and promote tumor growth and can lead to death, according to the release.

The reservoirs are located on the Klamath River near the Oregon border between Ashland, Ore., and Yreka, and are owned by PacifiCorp.

Recently, officials from the California Water Quality Control Board and the Office of Environmental Health and Hazard Assessment formed a Blue Green Algae Work Group. The work group published a document to provide guidance to local health officials dealing with toxic algae blooms.

Samples taken recently from Klamath reservoirs contained cell counts approximately 100 times greater than the threshold at which the BGA Work Group’s document recommends posting alerts to the public.

The algal blooms occur in the summer as the shallow, nutrient-rich water trapped behind the dams heats up and provides an optimal environment for the algae to bloom.