Portland District


Blue-green algae

Hazardous Algae Blooms: When in Doubt, Stay Out!Corps-managed reservoirs are among the many bodies of water in Oregon that experience blue-green algae blooms.

Blue-green algae occurs naturally in most water bodies, but
can develop into a bloom when warm, calm water and excess nutrients occur. Some blooms have the potential to produce toxins harmful to people and animals. Increased exposure leads to greater risk of side effects from these toxins. Because of this, the best advice is: When in doubt, stay out!

Observe water conditions before you swim, boat, water ski or recreate in or on the water. Don’t get into water that is foamy, scummy, thick (like paint), or has a pea-green, blue-green or brownish-red color. Many Oregon lakes, including Corps reservoirs, are not regularly tested for presence of blue-green algae toxins. The lack of a health advisory is not an indication that conditions are safe. Children and pets are at highest risk. Use your best judgment to keep your family and animals safe.


For health information or to report human or pet illnesses due to blooms, contact the Oregon Health Authority at 1-877-290-6767 or send an email to: hab.health@state.or.us

For more information

Call us: 503-808-4510

Email us for more information about our Harmful Algae Blooms policy.

To report a human or animal illness, contact the Oregon Health Authority at 877-290-6767 or via email to hab.health@state.or.us

Blue-green algae blooms: know the signs

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Portland District wants to provide recreational visitors with all the information needed to understand the potential risks associated with exposure to blue-green algae toxins. We want visitors to make responsible decisions for themselves about how much risk they are willing to take while recreating in the Corps' Oregon reservoirs. Information here and at recreation facilities provides details on identifying blue-green algae blooms and what precautions to take to reduce the risk of exposure. It is important for reservoir and river users to stay informed about potential harmful algae blooms, especially during the summer recreation season when blooms are most common.

Starting in 2015, we are no longer routinely monitoring and testing blue-green algae blooms at our reservoirs. Other federal, state and local agencies continue to monitor and test Blue River, Cougar, Detroit, Hills Creek, Lookout Point and Willow Creek reservoirs. 

However, because of different monitoring and testing protocols, lake and reservoir visitors need to take personal ownership of their health and safety, and never rely on the presence or absence of a public health advisory to determine if the water at any given lake or reservoir is safe. If in doubt, stay out!

A bloom is a rapid growth of cyanobacteria (also known as blue-green algae) that may produce harmful toxins. Algae are found in most water bodies, including lakes, reservoirs, ditches, ponds, streams and rivers. Often, the bloom is found near the shore due to wind or waves or sudden changes in water levels. Corps-managed reservoirs are among many bodies of water in Oregon that have experienced blue-green algae blooms.
Warm, calm water and excess nutrients contribute to the rapid growth of blue-green algae. Blooms can occur any time of the year, but are most common between June and September.
Harmful blue-green algae toxins can cause diarrhea, nausea, cramps, fainting, numbness, dizziness, tingling and paralysis if swallowed or inhaled. Skin contact can cause rashes or irritation. Risk increases with greater exposure or ingestion. Visit a medical care provider if you or someone you know becomes sick. Children, pets and people with compromised immune systems are at greatest risk. Eating fish caught during a bloom poses an unknown health risk.
  • Stay out of the affected water. 
  • Keep children and pets away. 
  • Never drink or cook with the affected water. Professional treatment is required to safely use affected water.
  • If you touch the affected water, wash thoroughly with another source of water.
  • Eating fish caught during a bloom poses an unknown health risk. If you choose to eat them, remove all fat, skin and organs before cooking because toxins are more likely to collect in these tissues.
The Corps of Engineers Portland District wants to keep boaters, swimmers and other visitors informed of potential risks from exposure to blue-green algae toxins.

The Portland District has revised its practice of routinely monitoring and testing blue-green algae blooms. While we want to decrease risk of exposure to potentially harmful blue-green algae toxins, it’s not possible to effectively monitor all of our reservoirs. We will continue to monitor and test selected reservoirs on a non-routine basis. If, as a result of these tests, blue-green algae toxins exceed Oregon Health Authority guidelines, visitors may see a public health advisory posted by the Oregon Health Authority on its website.

Visitors should not rely on public health advisories to determine whether or not the water is safe. We encourage visitors to learn how to identify blue-green algae blooms and how to protect themselves from the potential risks.

Extract from Corps' blue-green algae poster

Click the link here or the picture above to see posters describing the signs of algae blooms.