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In the Klamath Basin, blue-green algae blooms typically occur between June and October when temperatures rise, and water conditions are favorable for algal growth. Blue-green algae monitoring typically occurs from May to November. If river or lake conditions exceed public health standards for toxic algae, the area is posted with a health advisory sign.
Updated Posting Status
5/28/26- The Upper Klamath National Wildlife Refuge has been posted at Oregon's Advisory Level due to sample results for microcystin that exceeded Oregon Health Authority thresholds.
5/21/26- Upper Klamath Lake and Agency Lake have been posted at Oregon's Precaution Advisory Level due to visible blooms.
5/21/26- Sample results collected in Tule Lake for microcystin exceed the State of California’s Caution threshold and has been posted for the protection of public health.
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Advisories- For more information, please check California's HAB Incident Reports Map or Oregon's Cyanobacteria Advisories or their Recreational Advisory Map.
Satellite Imagery- Remotely sensed data from satellites can be used to estimate the spatial extent and concentration of both cyanobacteria and chlorophyll-a in large waterbodies. See California's Satellite HAB Map for the latest and historic estimates.
Updates- To get email updates about posting/deposting decisions and other notifications, email This email address is being protected from spambots. You need JavaScript enabled to view it. to join the Klamath Blue Green Algae Workgroup list serve.
About the Tracker
The BGA Tracker was built to inform the public and research community regarding river conditions. The Tracker utilizes current information to track the planktonic blue-green algae blooms throughout the Klamath Basin. The Blue-Green Algae Tracker identifies blue-green algae public health threats (i.e. exceeds health thresholds identified in the appropriate guidance) by river reaches bounded by public health monitoring locations.
River reaches which exceed applicable criteria for public health are indicated by different colors on the map that vary depending on the number of tiers within each jurisdiction's advisory thresholds. Advisory colors within the map are:
Oregon 
California 
Yurok Tribe 
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Blue-green Algae Official Notifications*
*As part of the Klamath Hydroelectric Settlement Agreement (KHSA) monitoring, notifications were sent out by sampling partners when monitoring results indicated a change to the posting status of waterbodies. Since the KHSA is no longer in effect, these notifications are no longer required, or produced. We retain them here as part of the historical record.
Other Information
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About Blue-green Algae
Blue-green algae (cyanobacteria) are a form of bacteria. Surface scums of blue-green algae are common in the summer months within reservoirs and along the Klamath River. Exposure to blue-green algae can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects. At high levels, exposure can result in serious illness or death. Small children and dogs are particularly susceptible due to their small body size and their potential to ingest water while recreating.
For a more detailed analysis of previous sampling seasons, please refer to the following document:
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Posting Guidelines
Advisory Threshold Guidelines
The Oregon Health Authority (OHA), California State Water Resources Control Board (SWRCB) and the Yurok Tribe each provide their own guidelines for posting advisories in recreation waters. Posting advisory thresholds recommended by the OHA, SWRCB and the Yurok Tribe are summarized in the following table and detailed in links below.
- Oregon - Public Health Advisory Guidelines: Harmful Algae Blooms in Freshwater Bodies (Updated in 2024)
- California
- Yurok Tribe - 2016 Posting Guidelines for Public Health Advisories
De-Posting Criteria
Postings should remain in place until the following criteria are met:
- Oregon
- If posting occurred due to visible scum – lift the posting if cyanotoxin results from the initial sample are below recreational use values (RUV).
- If posting occurred due to exceeding a toxin concentration guideline – lift the posting if cyanotoxin results are below RUV and either there is a commitment to continue bi-weekly sampling until the bloom is gone or bloom is visibly gone.
- California
- Quantitative samples confirm that all cyanotoxins are below all threshold levels AND declining bloom conditions continue for a minimum of two weeks.
- If posting was based on a Secondary Trigger, then either the secondary trigger OR primary triggers should no longer be exceeded (cell densities of toxin producers are below 4,000 cells/mL and no scums are visible.
- All evidence indicates the bloom is ending and favorable conditions are decreasing.
- Yurok Tribe
- Toxin Analysis- Two consecutive toxin sampling events (minimum of 1 week apart) with results below posting guidelines. (If the blue-green algae present is known to produce microcystin and anatoxin-a, it is recommended that both toxins be tested prior to lifting an advisory).
- No visible scums present.
- In some situations there may be reason, such as reported illness, to prolong the advisory beyond the recommended waiting period.
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Blue-green Algae Public Health Monitoring
Blue-green algae is monitored for potential risk to public health and to establish baseline condtions for Microcystis aeruginosa cell counts and microcystin toxin levels. Public health monitoring is conducted by PacifiCorp, Karuk Tribe, and Yurok Tribe. Public health monitoring occurs within the reservoirs (Copco and Iron Gate) and Klamath River mainstem from May - November. Copco and Iron Gate reservoirs are monitored once a month in May and twice per month from June through November (omitting August and September).The Klamath River mainstem from below Iron Gate dam to the estuary are monitored twice per month in June, July and October and weekly in August and September. Baseline monitoring is conducted by U.S. Bureau of Reclamation, PacifiCorp, Karuk Tribe, and Yurok Tribe from below Link Dam to the estuary. Baseline monitoring occurs monthly and seasonally from May - November. The blue-green algae tracker consists of both public health and baseline monitoring data. This monitoring effort is part of the Klamath Hydroelectric Settlement Agreement (KHSA) monitoring funded by PacifiCorp.
(Click on map to enlarge)
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Statewide Guidance on Harmful Algal Blooms recommends the following
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Health Advisory Posters
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Microcystin Toxin in Fish and Freshwater Mussels
Background
In an effort to better inform the public and tribal communities regarding potentially toxic algae (cyanobacteria) blooms, and toxins affecting fish and freshwater mussels, the Klamath Basin Monitoring Program has developed an on-line interactive map for tracking blue-green algae and toxins throughout the Klamath Basin. This work is supported by the Public Health component of the Klamath Hydroelectric Settlement Agreement (KHSA) funded by PacifiCorp. The public health monitoring region encompasses the mainstem Klamath River from Link Dam in Oregon to the estuary, in California including several mainstem tributaries. The monitoring is part of a multi-agency effort by the Bureau of Reclamation, PacifiCorp, Karuk, and Yurok Tribes to provide data on cyanobacteria and related toxins to support public health decisions.
During the summer months in the Klamath Basin blooms of toxigenic algae (Microcystis aeruginosa) and other related species of algae (Aphanizomenon flos-aquae, Anabaena flos-aquae, and Oscillatoria sp.) are common in Copco and Iron Gate Reservoirs. M. aeruginosaproduces a toxin, microcystin, a hepatotoxin which affects the liver. The toxigenic algae has been documented hundreds of miles downstream and in some years is found near the mouth of the Klamath River. Large blooms of M. aeruginosa create surface scums which may cover the entire surface of a waterbody (For a detailed map of monitoring locations and bloom conditions, please refer to the Blue-green Algae Tracker). Organisms such as fresh water mussels and yellow perch can ingest M. aeruginosa and there is the potential that the toxin can bioaccumulate in the tissue.
Freshwater Mussels
In 2007 and 2009, the Karuk and Yurok Tribes conducted tissue analysis of fresh water mussels collected from the Klamath River mainstem. The results indicated a seasonal pattern of microcystin congeners beginning in July and persisting through December. In 2009 levels of microcystin congeners found in fresh water mussels frequently exceed the lifetime* total daily intake for a child weighing 22 pounds. In some cases, a single meal of fresh water mussels posed an acute* exceedance of toxin. The 2009, study also revealed that, while concentrations of microcystin in the water column were below levels of concern, substantial microcystin bioaccumulation occurred at all study locations. The results of this study, partially funded by the KHSA monitoring, suggest that consumption of freshwater mussels from the Klamath River mainstem should be exercised with extreme caution.
For more information please refer to the following report:
*Acute Total Intake (250 ppb): single exposure event (e.g. week-end fishing trip). Seasonal Total Daily Intake (40 ppb): ongoing, “daily” exposure for several weeks during the cyanobacterial season. Lifetime Total Daily Intake (4 ppb): ongoing “daily” exposure for many months in settings where microcystin-producing cyanobacteria proliferate perennially.
Fish Tissue
In contrast to fresh water mussels, yellow perch sampled in Copco and Iron Gate Reservoirs in 2009 had no detectable levels of microcystin. However, the results from yellow perch sampled from Copco and Iron Gate Reservoirs have varied for microcystin over the past few years. Sampling conducted in the summer of 2007, found levels of microcystin in yellow perch fish tissue collected from Copco and Iron Gate reservoirs, exceeding the advisory level of 26 nanograms total microcystin/gram tissue. In 2008 PacifiCorp sampled yellow perch and crappie from Iron Gate and Copco Reservoirs, and rainbow trout from the Klamath River before, during, and after the bloom season; all tissue samples were non-detect for microcystin.
The presence of microcystin in fish tissue remains a health concern for the public and tribal communities.
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Related Links
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About Blue-green Algae
Blue-green algae (cyanobacteria) are a form of bacteria. Surface scums of blue-green algae are common in the summer months within reservoirs and along the Klamath River. Exposure to blue-green algae can cause rashes, skin and eye irritation, allergic reactions, gastrointestinal upset, and other effects. At high levels, exposure can result in serious illness or death. Small children and dogs are particularly susceptible due to their small body size and their potential to ingest water while recreating.
For a more detailed analysis of previous sampling seasons, please refer to the following document:
-
Posting Guidelines
Advisory Threshold Guidelines
The Oregon Health Authority (OHA), California State Water Resources Control Board (SWRCB) and the Yurok Tribe each provide their own guidelines for posting advisories in recreation waters. Posting advisory thresholds recommended by the OHA, SWRCB and the Yurok Tribe are summarized in the following table and detailed in links below.
- Oregon - Public Health Advisory Guidelines: Harmful Algae Blooms in Freshwater Bodies (Updated in 2024)
- California
- Yurok Tribe - 2016 Posting Guidelines for Public Health Advisories
De-Posting Criteria
Postings should remain in place until the following criteria are met:
- Oregon
- If posting occurred due to visible scum – lift the posting if cyanotoxin results from the initial sample are below recreational use values (RUV).
- If posting occurred due to exceeding a toxin concentration guideline – lift the posting if cyanotoxin results are below RUV and either there is a commitment to continue bi-weekly sampling until the bloom is gone or bloom is visibly gone.
- California
- Quantitative samples confirm that all cyanotoxins are below all threshold levels AND declining bloom conditions continue for a minimum of two weeks.
- If posting was based on a Secondary Trigger, then either the secondary trigger OR primary triggers should no longer be exceeded (cell densities of toxin producers are below 4,000 cells/mL and no scums are visible.
- All evidence indicates the bloom is ending and favorable conditions are decreasing.
- Yurok Tribe
- Toxin Analysis- Two consecutive toxin sampling events (minimum of 1 week apart) with results below posting guidelines. (If the blue-green algae present is known to produce microcystin and anatoxin-a, it is recommended that both toxins be tested prior to lifting an advisory).
- No visible scums present.
- In some situations there may be reason, such as reported illness, to prolong the advisory beyond the recommended waiting period.
-
Blue-green Algae Public Health Monitoring
Blue-green algae is monitored for potential risk to public health and to establish baseline condtions for Microcystis aeruginosa cell counts and microcystin toxin levels. Public health monitoring is conducted by PacifiCorp, Karuk Tribe, and Yurok Tribe. Public health monitoring occurs within the reservoirs (Copco and Iron Gate) and Klamath River mainstem from May - November. Copco and Iron Gate reservoirs are monitored once a month in May and twice per month from June through November (omitting August and September).The Klamath River mainstem from below Iron Gate dam to the estuary are monitored twice per month in June, July and October and weekly in August and September. Baseline monitoring is conducted by U.S. Bureau of Reclamation, PacifiCorp, Karuk Tribe, and Yurok Tribe from below Link Dam to the estuary. Baseline monitoring occurs monthly and seasonally from May - November. The blue-green algae tracker consists of both public health and baseline monitoring data. This monitoring effort is part of the Klamath Hydroelectric Settlement Agreement (KHSA) monitoring funded by PacifiCorp.
(Click on map to enlarge)
-
Statewide Guidance on Harmful Algal Blooms recommends the following
-
Health Advisory Posters
-
Microcystin Toxin in Fish and Freshwater Mussels
Background
In an effort to better inform the public and tribal communities regarding potentially toxic algae (cyanobacteria) blooms, and toxins affecting fish and freshwater mussels, the Klamath Basin Monitoring Program has developed an on-line interactive map for tracking blue-green algae and toxins throughout the Klamath Basin. This work is supported by the Public Health component of the Klamath Hydroelectric Settlement Agreement (KHSA) funded by PacifiCorp. The public health monitoring region encompasses the mainstem Klamath River from Link Dam in Oregon to the estuary, in California including several mainstem tributaries. The monitoring is part of a multi-agency effort by the Bureau of Reclamation, PacifiCorp, Karuk, and Yurok Tribes to provide data on cyanobacteria and related toxins to support public health decisions.
During the summer months in the Klamath Basin blooms of toxigenic algae (Microcystis aeruginosa) and other related species of algae (Aphanizomenon flos-aquae, Anabaena flos-aquae, and Oscillatoria sp.) are common in Copco and Iron Gate Reservoirs. M. aeruginosaproduces a toxin, microcystin, a hepatotoxin which affects the liver. The toxigenic algae has been documented hundreds of miles downstream and in some years is found near the mouth of the Klamath River. Large blooms of M. aeruginosa create surface scums which may cover the entire surface of a waterbody (For a detailed map of monitoring locations and bloom conditions, please refer to the Blue-green Algae Tracker). Organisms such as fresh water mussels and yellow perch can ingest M. aeruginosa and there is the potential that the toxin can bioaccumulate in the tissue.
Freshwater Mussels
In 2007 and 2009, the Karuk and Yurok Tribes conducted tissue analysis of fresh water mussels collected from the Klamath River mainstem. The results indicated a seasonal pattern of microcystin congeners beginning in July and persisting through December. In 2009 levels of microcystin congeners found in fresh water mussels frequently exceed the lifetime* total daily intake for a child weighing 22 pounds. In some cases, a single meal of fresh water mussels posed an acute* exceedance of toxin. The 2009, study also revealed that, while concentrations of microcystin in the water column were below levels of concern, substantial microcystin bioaccumulation occurred at all study locations. The results of this study, partially funded by the KHSA monitoring, suggest that consumption of freshwater mussels from the Klamath River mainstem should be exercised with extreme caution.
For more information please refer to the following report:*Acute Total Intake (250 ppb): single exposure event (e.g. week-end fishing trip). Seasonal Total Daily Intake (40 ppb): ongoing, “daily” exposure for several weeks during the cyanobacterial season. Lifetime Total Daily Intake (4 ppb): ongoing “daily” exposure for many months in settings where microcystin-producing cyanobacteria proliferate perennially.
Fish Tissue
In contrast to fresh water mussels, yellow perch sampled in Copco and Iron Gate Reservoirs in 2009 had no detectable levels of microcystin. However, the results from yellow perch sampled from Copco and Iron Gate Reservoirs have varied for microcystin over the past few years. Sampling conducted in the summer of 2007, found levels of microcystin in yellow perch fish tissue collected from Copco and Iron Gate reservoirs, exceeding the advisory level of 26 nanograms total microcystin/gram tissue. In 2008 PacifiCorp sampled yellow perch and crappie from Iron Gate and Copco Reservoirs, and rainbow trout from the Klamath River before, during, and after the bloom season; all tissue samples were non-detect for microcystin.The presence of microcystin in fish tissue remains a health concern for the public and tribal communities.
Related Links
