Cyanobacteria Harmful Algal Bloom Advisories

Cyanobacteria Harmful Algal Bloom Advisories

A golden lab sits on the bank of a blue-green lake

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Harmful algal blooms (HABs) can cause serious illness or death in pets and livestock that ingest water or mats containing high concentrations of cyanotoxins. Dogs can become 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, which led 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 and may be in the form of 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.

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Advisories Issued by Oregon Health Authority

Reminder: Not all Oregon waterways are monitored for cyanotoxins. A water body with no recreational health advisory does not mean that a bloom is not present. 

Advisories or precautions do not mean a body of water or an area is "closed." You can still enjoy the areas listed below while exercising caution with water exposure. OHA shares advisories to help people (especially those with young children) and pet owners to 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! 

Types of Advisories

  • Advisory: Cyanotoxin levels have been confirmed through testing to be unsafe for swimming and boating at speeds that cause water to spray into your face, OR a combination of conditions indicate that cyanotoxin levels may be unsafe for these activities. Toxin levels are unsafe for pets.
  • Precaution: A bloom has been confirmed or cyanotoxins are present but at levels that are safe for human recreation. Toxin levels may still be unsafe for pets.
  • Advisory downgraded to precaution: An 'advisory' is downgraded to a 'precaution' when water testing shows safe levels for human recreation, but a bloom or toxins are still present. Toxin levels may still be unsafe for pets.
  • Lifted: Testing shows cyanotoxins are not present, or when the bloom is visibly gone. 

Table: Oregon Health Authority

 

Maps

Oregon Harmful Algal Bloom Advisory Map

McKenzie Watershed Harmful Algal Bloom Monitoring Map

Advisories in Surrounding States

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 a harmful algae bloom 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 cyanobacteria toxins often develop rapidly. Death can occur within minutes to hours after exposure.

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Updated / Reviewed: November 4, 2026