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Oregon Department of Environmental Quality

Water Quality

Harmful Algal Blooms 

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Harmful Algal Blooms

Current information for Friday, Sept. 19, 2014

The Oregon Health Advisory has expanded a health advisory for a stretch of the Willamette River in Portland after preliminary test results showed the presence of toxic blue-green algae in the river.

The advisory extends from Ross island downriver to the south end of Sauvie Island. Officials  recommend people avoid all contact with Willamette water in this stretch of the river.

Check OHA’s Harmful Algae Bloom webpage for updates, Q & As, fact sheets and other information.

DEQ has assisted OHA by talking algal samples from the river, having them tested, and sending test results to OHA. These types of algal blooms occasionally appear in late summer. A combination of low river flow and warmer-than-usual temperatures this summer are the likely major contributors to the algae blooms currently visible.



Harmful algal blooms are caused by high concentrations of certain types of algae that produce toxic compounds. These blooms can cause sickness and death in humans, pets and livestock who come in contact with or drink the water. Oregon has several documented cases of dogs dying and humans becoming ill. The Oregon Health Authority (OHA) is the agency responsible for posting warnings and educating the public about harmful algal blooms. Once a waterbody is identified as having a harmful algal bloom, DEQ is responsible for investigating the causes, identifying sources of pollution and writing a pollution reduction plan.

Harmful algal blooms have occurred in a number of Oregon’s lakes, reservoirs and rivers. The blooms look different depending on local conditions. They can appear green, blue-green or reddish brown and form foam, slicks, scum or mats. 

DEQ's TMDL Harmful Algal Bloom Strategy

DEQ developed a Harmful Algal Bloom (HAB) strategy in 2011 to improve its abilities to address HABs and identify needs to improve this approach.


Most often harmful algal blooms are caused by cyanobacteria (aka blue-green algae). Algae are simple plants that are naturally occurring and form the base of the food webs. A small percentage of algae can produce toxic compounds.

Nutrient pollution, warm water, high pH, stagnant water and lots of sunlight can lead to excessive blooms. Nutrient pollution can come from wastewater treatment plants, residential on-site wastewater treatment systems, agricultural, urban and forestry runoff and natural sources. Introduced fish species also can recycle nutrients within a lake, allowing for more intense blooms. Warm water, high pH, stagnant water and sunlight are conditions that are harder to control in lakes and large rivers than nutrient pollution.

More information about specific lakes can be found in the Atlas of Oregon Lakes.


Most lakes and reservoirs have an agency which is responsible for managing recreation or drinking water. These agencies include the U.S. Forest Service, U.S. Army Corp of Engineers, lake associations and local government agencies.

When a potential harmful algal bloom is observed, these agencies will collect samples, document conditions and potentially post preliminary warning signs. Where there is not a management agency, such as some river sites, OHA, DEQ and local government agencies work together to respond. Sampling results are shared with OHA which will issue a recreational public health advisory when appropriate. OHA issues a press release, posts advisory information on its website and provides advisory signs.

OHA will lift an advisory when sampling indicates there is a low risk to public health. At lakes or river reaches with known recurring problems, management agencies may post year-round signs with educational information about harmful algal blooms.

Actions to Control and Eliminate

DEQ has the regulatory responsibility for restoring lakes and rivers to support recreation. DEQ tracks water bodies that don’t achieve water quality standards and develops pollution reduction plans. OHA and DEQ jointly develop drinking water protection plans. The state programs regulate pollution sources through water quality permits, licenses and certifications and nonpoint pollution source control. See DEQ's Harmful Algal Bloom strategy for evaluation of current programs and ideas for improvements.


Protecting high quality waters from harmful algal blooms is achieved by addressing the causes. DEQ does not allow discharge of wastewater to lakes or reservoirs. However, much more work needs to be done to identify waters at risk of developing harmful blooms.

Who to Contact about Harmful Algal Blooms

For  questions or concerns about harmful algal blooms, contact OHA. Also see OHA's website for a current list of waterbodies that have Harmful Algal Bloom warnings.


 Image of Odell Lake
Oregon waterbodies with OHA harmful algal bloom advisories through 2011 (click map to enlarge)

 Image of Odell Lake
2004 Anabaena bloom, a type of cyanobacteria, in Odell Lake (photo by Joe Eilers)

 Image of microcystis
Microscopic image of Microcystis, a type of cyanobacteria (Credit:


[print version]

For more information about DEQ's approach to Harmful Algal Blooms contact Dan Turner by phone at (503) 229-6982 or by email, or contact the appropriate Basin Coordinator.

Oregon Department of Environmental Quality
Headquarters: 811 SW Sixth Ave., Portland, OR 97204-1390
Phone: 503-229-5696 or toll free in Oregon 1-800-452-4011
Oregon Telecommunications Relay Service: 1-800-735-2900  FAX: 503-229-6124

The Oregon Department of Environmental Quality is a regulatory agency authorized to protect Oregon's environment by
the State of Oregon and the Environmental Protection Agency.

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