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 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, 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.

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 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.