Cyanobacteria Harmful Algae Bloom Advisories

Also known as toxic algae, cyanobacteria harmful algae blooms (HABs) can cause serious illness or death in pets and livestock that ingest water or mats containing high concentrations of cyanotoxins. Dogs can get extremely ill, and even die, within minutes to hours of exposure to cyanotoxins from drinking water, licking their wet fur or eating floating mats or dried crust along the shore. 

What to Watch For

A harmful algal bloom can look foamy, scummy, thick like paint, and pea-green or blue-green in color. It can look like a thick green or brownish-red mat, or bright green clumps suspended in the water. If you find thick, brightly colored foam, scum or mats in a lake, pond, river or stream—especially in shallow, marshy areas where cyanobacteria blooms can form—don’t let your pet drink or swim in the water. 

Benthic algal mats have been identified in the Columbia River, leading to the deaths of two dogs in 2024. Cyanobacteria that predominantly grow on the bottom (benthos) of waterbodies are referred to as “benthic cyanobacteria.” The color of the material is diverse, ranging from vibrant yellow-green and drab olive, to burgundy and dusky brown or black. The bloom material may also include non-toxic algae as many groups of cyanobacteria grow with algae—forming algal mats. The risk of exposure to benthic blooms increases significantly when the cyanobacteria mats dislodge from the bottom, become buoyant, and accumulate along shorelines, backwater channels, or eddies via wind or water current. 

This US Forest Service resource can help you tell the difference between normal algae and toxic algae.

The HAB photo guide from the California Water Quality Monitoring Council offers several photos of algal blooms. Pages 12-24 cover planktonic blooms (the kind usually seen in Oregon), and pages 25-36 focus on benthic mats (the kind seen on the Columbia). 

Eugene Water and Electric Board has an interactive Harmful Algal Bloom Monitoring Map for the McKenzie Watershed.

Active Advisories

Reminder: Not all Oregon waterways are monitored for cyanobacteria. 

Owners should be aware of the potential exposure to their pets while at these areas. Toxins cannot be removed by boiling, filtering or treating water with camping-style filters. Remember, when in doubt, stay out! 

Precautionary Status: A bloom has been sighted and water sampling is unavailable within 1 business day due to limited resources. Oregon Health Authority will issue pre-emptive public warnings following reports of dog illnesses or deaths possibly resulting from cyanotoxin exposure.

Oregon 
 

• South Umpqua River: The advisory covers the South Umpqua River from Canyonville downstream to the confluence with the mainstem Umpqua River, and the mainstem Umpqua River downstream past Elkton to Sawyers Rapids. Pools in the bedrock along the rivers edge are known to develop cyanobacteria (blue-green algae) blooms that can be harmful to pets and people if accidental ingestion occurs. PERMANENT ADVISORY

Lifted Advisories

Illness in pets can still occur at lower toxin values, so please continue to exercise caution with pets at these areas:

• Gerber Reservoir in Klamath County LIFTED 12.23.25
   
• Upper Klamath Lake in Klamath County LIFTED 12.23.25
  Water monitoring has confirmed the level of cyanotoxins in Upper Klamath Lake are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Thief Valley Reservoir in Baker and Union Counties due to elevated microcystin levels LIFTED 12.23.25
  Water monitoring has confirmed that the level of cyanotoxins in Thief Valley Reservoir are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Prineville Reservoir in Crook County LIFTED 12.23.25
  Water monitoring has confirmed that the level of cyanotoxins in Prineville Reservoir are below recreational guideline values for people and below safety values for dogs.
   
• Brownlee Reservoir in Baker County LIFTED 12.18.25
  Water monitoring has confirmed that the level of cyanotoxins in Brownlee Reservoir are below recreational guideline values for people. However, levels detected may still above OHA’s educational guideline values for dogs. Pet owners should therefore keep their pets away from areas that have the appearance of a cyanobacteria bloom.
   
• Barnes Unit of Upper Klamath National Wildlife Refuge in Klamath County LIFTED 12.3.25
  Hunters should avoid using contaminated water for cleaning gear or handling harvested birds. Dogs are at increased risk for cyanobacteria exposure because of their size and level of activity. They can become extremely ill and die from water intoxication after drinking excessive amounts of water while swimming or fetching objects for long periods of time.
   
• North & South Tenmile Lakes in Coos County LIFTED 12.3.25
   
• Upper Klamath National Wildlife Refuge in Klamath County LIFTED 12.3.25
  Water monitoring has confirmed that the level of cyanotoxins in Upper Klamath National Wildlife Refuge is below recreational guideline values for people. However, detected levels are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Wapato Marsh at Oaks Bottom Wildlife Refuge in Multnomah County LIFTED 12.2.25
  Water monitoring has confirmed that the level of cyanotoxins in Wapato Marsh at Oaks Bottom Wildlife Refuge are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Hells Canyon Reservoir in Baker and Wallowa Counties LIFTED 11.18.25 
  Water monitoring has confirmed that the level of cyanotoxins in Hells Canyon Reservoir are below recreational guideline values for people. However, levels detected may still above OHA’s educational guideline values for dogs. Pet owners should therefore keep their pets away from areas that have the appearance of a cyanobacteria bloom.
   
• Bully Creek Reservoir in Malheur County LIFTED 11.7.25
  Water monitoring has confirmed that the level of cyanotoxins in Bully Creek Reservoir are safe for human health and pet health.
   
• Powder Arm of the Brownlee Reservoir in Baker County LIFTED 11.7.25
  Water monitoring has confirmed that the level of cyanotoxins in Powder Arm of Brownlee Reservoir are safe for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Unity Reservoir in Baker County due to the presence of a microcystin above healthy levels for recreation.LIFTED 11.7.25
  Water monitoring has confirmed that the level of cyanotoxins in Unity Reservoir are safe for human health and pet health.
   
• Devil's Lake in Lincoln County LIFTED 10.21.25
   
• Eckman Lake in Lincoln County LIFTED 10.21.25
  Water monitoring has confirmed that the level of saxitoxin in Eckman Lake are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Oswego Lake in Clackamas County LIFTED 10.15.25
  Water monitoring has confirmed that the level of cyanotoxins in Oswego Lake are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Smith Reservoir in Klamath County LIFTED 10.7.25
   
• Ochoco Lake in Crook County LIFTED 9.30.25
  Water monitoring has confirmed that the level of cyanotoxins in Ochoco Lake are below recreational guideline values for people. However, levels detected are still above OHA’s educational guideline values for dogs, and owners should keep their pets away from these areas.
   
• Ross Island Lagoon in the Willamette River in Multnomah County LIFTED 9.16.25
   
• Haystack Reservoir in Jefferson County LIFTED 9.15.25
   
• Cullaby Lake in Clatsop County LIFTED 9.5.25
   
• Lake Simtustus in Jefferson County LIFTED 8.29.25
   
• Odell Lake in Klamath County LIFTED 8.26.25
  Water monitoring has confirmed that the level of cyanotoxins in Odell Lake are below recreational guideline values for people. However, levels detected are still above OHA’s safety values for dogs, and owners should keep their pets away from the lake.
   
• Antelope Flat Reservoir in Crook County LIFTED 8.19.25
   
• Ross Island Lagoon, and the Willamette River to include Ross Island Bridge downriver to Wapato Bridge and Kelley Point Park in Multnomah County LIFTED 8.19.25
  Water monitoring has confirmed that the level of cyanotoxins in Ross Island Lagoon and the Willamette River south of the lagoon downriver to Wapato Bridge and Kelley Point Park are below recreational guideline values for people. Owners should still exercise caution with pets at the river.
   
• Lake Owyhee (northern portion, starting at Indian Creek Campground extending to the reservoir outflow) in Malheur County LIFTED 7.30.25
   
• Devil's Lake in Lincoln County LIFTED 7.21.25
   
• Prineville Reservoir in Crook County LIFTED 7.1.25
   
• Lost Creek Lake in Jackson County LIFTED 7.1.25
  Water monitoring has confirmed that the level of cylindrospermopsin in Lost Creek Lake is below recreational guideline values for people. Owners should still exercise caution with pets at the lake.
   
• Lake Billy Chinook in Jefferson County LIFTED 7.1.25
  Water monitoring has confirmed that the level of microcystin in Lake Billy Chinook is below recreational guideline values for people. However, levels detected are still above OHA’s safety values for dogs, and owners should keep their pets away from these areas.
   
• Fern Ridge Reservoir in Lane County LIFTED 6.24.25
  Water monitoring has confirmed that the level of cyanotoxins in Fern Ridge Reservoir are below recreational guideline values for people.
   
• Emigrant Lake in Jackson County LIFTED 5.9.25
   
• Crane Prairie Reservoir in Deschutes County LIFTED 6.13.25

Local HAB Map

• McKenzie Watershed

Advisories in Surrounding States

• California
• Idaho
• Nevada
• Washington

Children and Pets are Particularly Susceptible

The most common toxins in harmful algal blooms in Oregon are microcystins and cylindrospermopsin. Exposure to these toxins can produce symptoms of numbness, tingling and dizziness that can lead to difficulty breathing or heart problems and require immediate medical attention. Symptoms of skin irritation, weakness, diarrhea, nausea, cramps and fainting should also receive medical attention if they persist or worsen. Children and pets are particularly susceptible.

Swallowing or inhaling water droplets should be avoided, as well as skin contact with water by humans or animals. Drinking water from affected bodies of water is especially dangerous. Toxins cannot be removed by boiling, filtering or treating the water with camping-style filters.

Oregon Public Health recommends that people who choose to eat fish from waters where algae blooms are present should remove all fat, skin and organs before cooking since toxins are more likely to collect in these tissues.

Symptoms in Dogs

Exposure to toxic blue-green algae can result in:

• Weakness or collapse
• Nausea, vomiting
• Excessive drooling
• Weakness, fatigue, stumbling
• Abdominal pain
• Diarrhea
• Difficulty breathing
• Shaking, trembling
• Seizure like activity—tremors, rigidity, paralysis
• Liver failure

If your dog goes into the water:

• Don’t let your pet lick its fur.
• Wash your pet with clean water as soon as possible.
• If your dog has symptoms such as drooling, weakness, vomiting, staggering and convulsions after being in water, seek immediate veterinary care. Acute, life-threatening symptoms from cyanobacterial toxins often develop rapidly. Death can occur within minutes to hours after exposure.