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Be aware of cyanobacterial (harmful algae) blooms this summer

May 8, 2019

Increasing temperatures create potential for cyanotoxins in water

As summer approaches, the Oregon Health Authority reminds people heading outdoors to be on the lookout for toxin-producing cyanobacterial blooms when recreating in Oregon lakes, rivers and reservoirs.

Because cyanobacterial blooms are naturally occurring worldwide, they can form in any water body. Many blooms are harmless, but under the right conditions — when weather, sunlight, water temperature, nutrients and water chemistry are ideal — they can produce cyanotoxins that make people and animals sick.

If a water body is being sampled and toxin levels are found above OHA health safety levels, OHA issues a recreational use health advisory warning people to stay out of water to avoid illness.

Since only a fraction of Oregon’s fresh waters are monitored, OHA suggests people stay out of the water if it looks foamy, scummy, thick like paint and pea-green, blue-green or brownish-red in color. Exposure to cyanotoxins can cause diarrhea, cramps, vomiting, numbness, dizziness and fainting.

"You are your own best advocate when it comes to knowing what to look for and when to stay out of areas where water is affected by a bloom," said Rebecca Hillwig, natural resource specialist with Environmental Public Health at OHA. "Our motto is: When in doubt, stay out."

Children and pets are particularly sensitive to illness because of their size and activity levels. Within hours of exposure to cyanotoxins by drinking the water, licking their fur or eating the toxins from floating mats or dried crust along the shore, dogs can get extremely ill and even die.

A permanent recreational use advisory for the South Umpqua River and mainstem Umpqua River from Lawson Bar down to Elkton has been in place since 2012. Starting in 2009 multiple dog deaths resulted from the animals drinking the water and licking toxins from potholes along the riverside.

Although cyanotoxins are not absorbed through the skin, people with sensitive skin can develop a rash when wading, playing or swimming in or around a bloom. More serious symptoms occur when water is swallowed while swimming, or when water droplets are inhaled during high-speed activities such as water-skiing or wakeboarding.

Cyanobacterial blooms have been occurring since early in Earth’s history. However, global climate change is likely to increase opportunities for cyanobacteria to grow. Warmer water temperatures, changes in acidity and new rainfall patterns are expected to increase how often and how long cyanobacterial blooms occur and could increase cyanotoxin production.

People can continue visiting their favorite lakes, rivers or reservoirs, and enjoying activities such as camping, hiking, biking, picnicking, and bird watching by staying aware of signs of a bloom and taking precautions when a bloom is suspected. It is also safe to enjoy some water activities such as canoeing, fishing and boating as long as speeds do not create excessive water spray.

To learn if an advisory has been issued or lifted for a sampled water body, visit the Harmful Algae Bloom website or call the Oregon Public Health Division toll-free information line at 877-290-6767.

For health information or to report an illness, contact OHA at 971-673-0400. For campground or lake information, call the local management agency.


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Delia Hernández

OHA External Relations


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