Blue-green algae

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. 


Blue-green algae occurs naturally in most water bodies--including Corps-managed reservoirs--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!

Children and pets are at highest risk. Use your best judgment to keep your family and animals safe. 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. 

Because of different monitoring and testing protocols, lake and reservoir visitors should not rely on public health advisories to determine whether or not the water is safe. 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. We encourage visitors to learn how to identify blue-green algae blooms and how to protect themselves from the potential risks. If in doubt, stay out!



What is a harmful algae bloom?
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.

What causes 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.

What are the dangers of blue-green algae?
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.

What precautions should visitors take to protect themselves?
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.


Extract from Corps' blue-green algae poster