Harmful Algal Blooms and Drinking Water in Oregon

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Harmful algal blooms are a major environmental problem in all 50 states.


Harmful algal blooms affect aquatic ecosystems, endangered species, and drinking water supplies. They are increasingly a public health hazard, and future climate conditions are expected to produce even more favorable conditions for the growth of cyanobacteria, leading to earlier, more frequent, and larger algal blooms.

Over the past decade, various cyanotoxins including microcystins, anatoxin-a, and cylindrospermopsin have been detected in the surface waters of rivers around Oregon, including the Clackamas, North Santiam, and Tualatin River systems, which are important drinking water sources for a substantial number of Oregon’s residents. Harmful blooms have resulted in numerous water contact and recreational closures and health advisories in lakes, reservoirs, and rivers; dog deaths have been associated with exposure to cyanotoxins. Cyanobacterial blooms produce a range of materials (geosmin, organic matter, toxins) that are a threat to the quality of drinking water supplies and impose an increased burden on drinking water providers for monitoring and treatment. These issues are harder to address in a timely and effective manner when the sources and nature of the blooms are not entirely known.


algal bloom

Algal bloom in the Ross Island Lagoon, Willamette River, Oregon (Photo: Kurt Carpenter, USGS).

Cyanobacteria and Harmful Blooms (HABs)

Cyanobacteria are a ubiquitous and vital part of Earth's ecosystem, producing atmospheric oxygen through their photosynthesis for billions of years. Today, cyanobacteria continue to share vast amounts of oxygen from their photosynthesis in the ocean and are an important part of many aquatic food webs. They may “fix” atmospheric nitrogen that enhances crop yields and agricultural production. But under certain conditions, when nutrients, light, and proper habitat converge, cyanobacteria often grow into noxious and toxic harmful blooms (HABs) that threaten water quality, drinking water, endangered species and other aquatic life, and human health.

HABs occur in many different types of waterbodies, including drinking water reservoirs, lakes, and other ponded waters. In these environments, cyanobacteria outcompete other algae when the surface warms and the waterbody temperature stratifies. Under these conditions many types of algae sink into the dark depths, whereas the more "buoyant" cyanobacteria (which are rich with gas vesicles) remain higher in the water column, closer to the sun.

Blooms of cyanobacteria may also occur in rivers, both as suspended “seston” in large flowing rivers, as well as extensive growths along riverbeds and channel margins. The basal forms of cyanobacteria form slimy filamentous mats (Microcoelus, Oscillatoria, Phormidium), and globular or “ear” shaped rubbery colonies of Nostoc, which are found on rocks, logs, and freshly exposed faces of basalt. These growths are observed in the rivers draining the Western Cascades that are vital to Oregon’s population for providing municipal drinking water.

While not all cyanobacteria blooms are toxic, they may produce an array of compounds including potent liver toxins (hepatotoxins, such as microcystins and cylindrospermopsins) and neurotoxins (anatoxin-a and saxitoxin, for example) that are especially dangerous to dogs, and even large animals including sheep, mountain goats, and cattle. Cyanobacteria also produce lipopolysaccharides that are skin irritants and may pose other concerns for water contact recreationists. Cyanobacteria also produce compounds that can foul water supplies with unpleasant tastes and odors. HABs are increasingly a public health hazard, with increased efforts to combat HABs at the federal and state levels, including Oregon, California, and Washington.


lake profiler

Lake profiler deployed on Detroit Lake, Oregon, to study harmful algal blooms in the reservoir (Photo: David Weathers, USGS).

HABs in Oregon

In Oregon, HABs have potential to impact revenue from recreation, with numerous popular waterbodies having multiple advisories over the past decade due to HABs and the toxins they produce, including Detroit Lake, Timothy Lake, Tenmile Lake, Odell Lake, Upper Klamath Lake, and many others. HABs are not limited to one or two types of waterbodies; blooms of Dolichospermum (formerly Anabaena) are common in the large water storage reservoirs on the Willamette’s tributaries, and in several lakes in Lincoln and Clatsop Counties (Cullaby, Carnahan, Ten Mile, and Devils Lake, for example) where Gloeotrichia, Aphanizomenon, Microcystis, and other cyanobacteria can bloom during summer months. HABs in small agricultural (nursery) irrigation ponds have also led to releases of cyanotoxins downstream, sometimes impacting drinking water intakes. And in central Oregon, various stock ponds and reservoirs used for livestock watering have experienced HABs with resulting deaths of cattle. In one incident in 2017, 32 cattle perished near Lakeview.

Harmful algal blooms (HABs) have occurred in many of the large water storage reservoirs in the Willamette River Basin, resulting in health advisories for water contact recreation, and in 2018 for the first time in Oregon, a drinking water advisory due to cyanotoxins. A HAB in Detroit Lake during spring produced cyanotoxins that were transported downstream in the North Santiam River, affecting the State capital of Salem's drinking water for about a month. Similar types of cyanobacterial blooms occur in Blue River and Cougar Reservoirs, in the McKenzie River Basin, with similar threats to drinking water for the City of Eugene.

To address this issue, and to complement on-going limnological surveys, the USGS partnered with the City of Salem, the Eugene Water and Electric Board, and the U.S. Army Corp of Engineers to monitor algal blooms in Detroit Lake and nearby Cougar Reservoir - and the downstream rivers - using continuous water-quality monitors that transmit data to water treatment plant operators, dam operations, researchers and the public in near real-time.

Basic parameters, including water temperature, conductance, and turbidity, are collected vertically in the reservoirs approximately every meter for the top 10 meters, then every 5 meters down into the hypolimnion (bottom waters) to a maximum of 75-90 meters (230-295 feet) deep. HAB parameters include surrogates for algal biomass (total chlorophyll [fCHL] and blue-green pigment phycocyanin [PC]), indicators of photosynthetic activity (dissolved oxygen and pH) and fluorescing dissolved organic matter [fDOM] that is often a reliable surrogate for dissolved organic carbon. Each of these parameters is monitored hourly at the surface (~1-meter depth) and through the water column multiple times per day from locations near dams (at the log booms).

View Profile Analysis Tool - Detroit Lake, OR

Data are available (per parameter) as: 

  • Profiles with a slider scale to portray conditions with depth over time
  • Time-series plots, based on the hourly data collected at 1-meter depth
  • Contours, color plots of parameter values by depth over time.

Cyanobacterium Gloeotrichia echinulata under a microscope (Photo: Barry Rosen, USGS).

When taken together with the downstream continuous water-quality monitors these data provide an early-warning indicator of an algal bloom in the reservoir, or the possible release and transport of algae downstream to drinking-water intakes. These data also provide insights into the evolution, behavior, and decay of the seasonal blooms which can inform management strategies, modeling, and perhaps prediction of blooms in the future.


USGS Laboratory Capabilities

The USGS Oregon Water Science Center has researched and implemented methods for the evaluation of cyanotoxins in water and in the cyanobacteria colonies on rock substrates and in river and lake/reservoir plankton. These included the use of passive samplers (Solid Phase Adsorption Toxin Trackers, or SPATTs), which concentrate cyanotoxins from the water column over time; these can be extracted and analyzed using Enzyme Linked Immunosorbent Assays (ELISA). Cyanotoxins currently analyzed at the USGS include total microcystins/nodularin (ADDA), cylindrospermopsin, saxitoxin, and anatoxin-a. Chlorophyll-a is also measured in the laboratory as an estimate of the total algal biomass in water, benthic, and plankton net tows.


Additional Resources

Oregon Health Authority

U.S. Environmental Protection Agency


Although not an algal bloom, dense stands of rooted macrophytes can also impair habitat and degrade water quality. Here the native Water Stargrass (Heteranthera dubia) nearly fills the channel in the Yakima River, Washington, where it contributes to large swings in pH and dissolved oxygen (Photo: Kurt Carpenter, USGS).