Skip to Main Content View Text-Only

The City of Portland, Oregon

Portland Water Bureau

From forest to faucet, we deliver the best drinking water in the world.

Customer Service: 503-823-7770


More Contact Info

Subscribe to RSS feed

Most Recent

View Less

Cyanotoxins and Algae

What are cyanotoxins?

Cyanotoxins are a type of toxin, or harmful substance, that are produced by certain types of algae that grow in some lakes and rivers. There is only one group of algae, called cyanobacteria, that can produce toxins.  Cyanobacteria are commonly found throughout the U.S. in low numbers. However, cyanobacteria can become harmful to health when, under certain environmental conditions, toxin-producing cyanobacteria bloom and release toxins into the water. Not all cyanobacteria produce toxins and even then, those that are able to produce toxins do not always do so.

Does the Portland Water Bureau test for algae?

Yes. The Portland Water Bureau tests Bull Run source water for algae on a weekly-basis. There are many types of algae detected in the Bull Run source water and they vary throughout the year. Levels of algae that do not produce toxins increase on a seasonal basis. These types of algae do not pose a health risk, but can have the potential to affect the taste or smell of the water, or clog home or building filters.

Has there ever been a cyanobacteria bloom in the Bull Run source water?

No, Portland Water Bureau is fortunate to have a surface water source, the Bull Run Watershed, that has never had a cyanobacterial bloom and is not vulnerable to the environmental conditions that would encourage and support a cyanobacterial bloom. The Bull Run Watershed is naturally low in nutrients, leading to oligotrophic conditions and low biological productivity in Portland’s water supply reservoirs. Additionally, due to strict protections for the watershed itself, there are no typical sources of nutrient pollution, such as agriculture, recreational use, livestock grazing, or commercial or residential development contributing additional nutrients to the reservoirs. Due to these conditions, Bull Run source water is not vulnerable to cyanobacterial blooms and resulting health issues.

Are there state or federal rules that regulate cyanotoxins in drinking water?

The State of Oregon recently passed temporary rules that require drinking water systems to test for cyanotoxins starting July 15, 2018. The Portland Water Bureau is required to follow these rules and routinely tests for cyanotoxins in the Bull Run source water accordingly. Currently, there are no rules at the federal level.  However, the Environmental Protection Agency (EPA) recognizes that cyanotoxins may require federal regulations and is requiring drinking water providers around the country to collect data about cyanotoxins through the Unregulated Contaminant Monitoring Rule 4 (UCMR4). Based on the results from this monitoring, the EPA may decide to create federal rules that regulate cyanotoxins in drinking water.

Has the Portland Water Bureau tested for cyanotoxins?

Yes, the Portland Water Bureau voluntarily tested Bull Run source water for cyanotoxins in 2005 and June 2018, and tests water routinely as required by the new State of Oregon rules. Additionally, the Portland Water Bureau is preparing to test for ten different cyanotoxins in Summer 2019 as part of the federal Unregulated Contaminant Monitoring Rule 4 (UCMR4). The Portland Water Bureau has only had one detection of cyanotoxins. In 2005, a cyanotoxin was detected in one sample at 0.020 ppb, well below the current vulnerable population health advisory level of 0.3 ppb.

What would the Portland Water Bureau do if cyanotoxins were detected in the raw water testing?

If cyanotoxins were detected in the raw water testing, Portland would conduct more extensive testing in both the raw water and treated drinking water as it enters town. Based on the results of those tests, and in consultation with public health officials, the Portland Water Bureau would notify the public if the level of cyanotoxins pose a public health risk. The Portland Water Bureau may be able to make operational changes to minimize cyanotoxin levels and may have the flexibility to use its high-quality groundwater source, the Columbia South Shore Well Field. The well field is not at risk for any type of algal contamination since algae does not grow in groundwater.

How can customers prepare for a cyanotoxin-related drinking water advisory?

The risk of the Portland Water Bureau issuing a drinking water advisory related to cyanotoxins is low. However, the Portland Water Bureau encourages customers to store an emergency supply of water in case of emergencies when drinking water may not be available. These could include drinking water advisories, planned shutdowns for Portland Water Bureau construction, or in the event of a major earthquake. More information about storing water can be found on the Regional Water Providers Consortium page:

The Portland Water Bureau also encourages all customers to register for Public Alerts to receive emergency alerts from the Portland Water Bureau and other City of Portland entities. Customers can register at

More information about cyanobacteria and cyanotoxins can be found on the Oregon Health Authority and Environmental Protection Agency websites.