Experts Warn Against Swimming in Oregon’s Legendary Willamette River Due to Toxic Algae

Written by Sharon Parry
Published: August 14, 2023
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As the heatwave continues to burn in Oregon, there is worse news for residents looking for a place to cool down. The Oregon Health Authority has issued urgent advice on the dangers of taking a dip in the Willamette River and Sauvie Island areas. This follows a previous recreational use advisory issued a couple of days before that warned of toxic algae bloom developing in these bodies of water.

The health authority website provides a useful list of all current cyanobacteria bloom advisories which is continually updated. There’s no denying the terrible timing as temperatures are predicted to soar to over 100 degrees before falling back to the 90s. Nevertheless, it’s just too dangerous to enter the water with an algae bloom affecting the river in Downtown Portland between the Ross Island Lagoon and the Riverplace Marina. The greatest risks are for children and pets.

Help is at hand! Whilst the natural water courses may be out of bounds, there is a useful list of ‘misting stations’ in parks where residents can cool off in a drizzle of safe water.  

What Are Toxic Algae Blooms?

Confusingly, toxic algae blooms are not caused by algae. There is a rapid growth of a type of primitive bacteria called cyanobacteria and which are also called ‘cyanobacterial blooms’. This type of bacteria is naturally present in freshwater and saltwater and plays a vital role in ecosystems. The problem is that low water levels, an excess of nutrients, and possibly other factors that we do not yet understand can cause ‘blooms’. These may be harmless but some cyanobacteria produce harmful toxins called cyanotoxins. The common toxins in Oregon are microcystins and cylindrospermopsin.

How Toxic Algae Blooms Make You Ill

Toxins enter the body in four ways. The most obvious is through ingestion which is drinking contaminated water and eating food contaminated by the water. For dogs, this could also be licking their wet fur. Another route is through breathing in tiny droplets (aerosolized toxins) caused by the water being agitated. Skin contact can cause a rash and eye contact can irritate.

Symptoms of Cyanotoxin Exposure in Humans

Cyanotoxin exposure symptoms usually start within 24 to 72 hours after swallowing or inhaling the water. It can feel very like food poisoning. You may have headaches, cramps, diarrhea, nausea and vomiting, numbness, dizziness, and fever. If it lasts for more than 72 hours, you should seek medical attention.

Symptoms of Cyanotoxin Exposure in Dogs?

Dogs are often sniffing and licking at the water’s edge and are more likely to be exposed. They will probably experience diarrhea, vomiting, breathing problems, difficulty walking and standing, or loss of appetite. It takes only small quantities of the toxin to make a dog very ill. So, if your dog shows any of these symptoms, get them to a vet right away.

Happy rottweiler puppy running and playing on a beach at sunset. Cute little dog jumping and splashing water. Sand play.

Dogs can ingest cyanotoxins by licking and chewing objects contaminated with water.


Things You Cannot Do in Water Affected by Algae Blooms

When an advisory for toxic algae is in place, you and your children should not swim in the water. Also, avoid high-speed activities such as power boating or water skiing that could create aerosols. Keep your pets out of the water too, this will probably mean keeping your dog on a leash so that you can control them properly.

If you are camping or living outside, do not drink the water. That includes drinking river water that has been boiled, filtered, or treated with camping-style filters – these will not remove the toxins.

Things You Can Do in Water Affected by Cyanobacterial Blooms

There are still ways in which you can enjoy the water and surroundings. You can hike, jog, ride bikes, picnic and bird watch in the areas. You can even boat on the water as long as you are using canoes and kayaks or other boats that do not create a lot of spray. Taking pictures is fine!

The photo featured at the top of this post is © Aleksandrkozak/

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About the Author

Dr Sharon Parry is a writer at A-Z animals where her primary focus is on dogs, animal behavior, and research. Sharon holds a PhD from Leeds University, UK which she earned in 1998 and has been working as a science writer for the last 15 years. A resident of Wales, UK, Sharon loves taking care of her spaniel named Dexter and hiking around coastlines and mountains.

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