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Federal, state and tribal authorities advise caution on dangerous Klamath River algae

Release Date: 9/30/2005
Contact Information: Mark Merchant, U.S. EPA, (415) 947-4297; or William L. Rukeyser, California State Water Resources Control Board, (916) 341-7365

SAN FRANCISCO – In response to the emergence of dangerous algal blooms in the Klamath River in California, the Karuk Tribe, the North Coast Regional Water Board and the U.S. Environmental Protection Agency are joining other local, state and federal agencies in warning residents and recreational users of the river to use caution when near such blooms.

Klamath River “This algae produces toxins that pose a significant potential public health concern. We advise people to avoid all direct contact with Klamath River water while the bloom is occurring.” said Alexis Strauss, Water Division director of the EPA’s regional office in San Francisco.

Water samples taken over the past two months from Copco and Iron Gate Reservoirs – located on the Klamath near the Oregon border – have revealed high levels of the toxic blue-green alga Microcystis aeruginosa. Blooms of Microcystis aeruginosa, which often occur between June and September, can look like green, blue-green, white or brown foam, scum or mats floating on the water. They have been found as far as 125 miles downstream of the reservoirs.

The Klamath River is rich in nutrients that support the growth of the blue-green algae. Warm and calm surface water created by Iron Gate and Copco Reservoirs provide an ideal environment for the growth of large algal blooms. The extent of the blooms, and their toxicity, were not known until studies were conducted this year by the Karuk Tribe.

Water samples collected in Copco and Iron Gate reservoirs. “In August, we found levels of Microcystis aeruginosa as high as 46.8 million cells/ml along the shoreline and 8.9 millions cells/ml on the open water. These levels exceed the World Health Organization (WHO) standard for recreational use by 468 and 89 times, respectively,” explained Susan Corum, the Water Resources Coordinator for the Karuk Tribe’s Department of Natural Resources. “Microcystin toxin produced by the blooms in these locations was 1571.7 and 436.9 μg/L; exceeding the WHO Tolerable Daily Intake level by 217 and 60.3 times respectively. These levels are among the highest recorded in the United States.”

According to California’s Office of Environmental Health Hazard Assessment (OEHHA), the U.S. EPA, the Karuk Tribe and Water Board, the Microcystis aeruginosa and resulting microcystin toxin pose a significant potential health threat to humans and animals exposed through direct ingestion of contaminated water or incidental ingestion during recreational water activities and bathing.

“The public needs to take the microcystin toxin in this algae seriously,” said Catherine Kuhlman, Executive Officer of the North Coast Water Board. “The levels of algae and associated toxins measured in parts of the river are high enough to pose health risks to anyone drinking or bathing in the water, particularly children and animals.”

Studies of the possible health effects of exposure to Microcystis aeruginosa and its microcystin toxin in the Klamath’s waters range from mild, non-life threatening skin conditions to permanent organ impairment and death depending upon exposure time and intensity.

Symptoms could include mild to severe eye irritation, allergic skin rash, mouth ulcers, fever, cold and flu-like symptoms, vomiting, diarrhea, kidney damage, liver damage or complete failure, and death.

Children and animals are at the greatest risk of adverse effects, due to their smaller body size and higher water ingestion rates.

As pets and other domestic animals could drink contaminated water, pets and livestock should be kept away from the water.

There are three main ways to be exposed to Microcystis aeruginosa and subsequent microcystin toxins in contaminated waters:

  • direct contact to exposed skin or to the highly sensitive membranes of the ear, eye, nose and throat;
  • accidental or intentional swallowing; and;
  • inhalation of contaminated water aerosols.

Algae blooms at Mallard Cove on Copco Reservoir A full-grown adult ingesting 3.4 ounces of contaminated water in a given day would be exposed to levels 28 times greater than the accepted World Health Organization’s Tolerable Daily Intake value. This calculation is based on a single one-hour “swimming event” per day. More swimming events or activities of longer duration could result in greater exposure.

For an average-size child who is 3-years-old, ingesting slightly more than a measuring cup of contaminated water in any one “swimming event” would be the equivalent of 278 times the accepted WHO Tolerable Daily Intake value. As with adults, more swimming events or activities of longer duration could result in greater exposure.

Local, state, tribal and federal health and environmental agencies recommend that people not drink or cook with contaminated waters. You should avoid or minimize contact with contaminated waters. It is best of stay out of the water near algal blooms and to keep pets away. If you do come in contact with the water, wash thoroughly with clean water. Avoid eating fish caught during an algal bloom. If you do, fishermen should clean the fish with fresh water and dispose of the innards away from the river or where animals could eat them; Avoid irrigation with contaminated water; Report dead or distressed wildlife along the shoreline to local, state or tribal authorities.

    For more information, visit: The 1999 World Health Organization, Toxic Cyanobacteria in Water: A guide to their public health consequences, monitoring and management at: and,
    World Health Organization Guidelines for Drinking Water Quality, 3rd Edition at: