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Summer Drought Increases Chances of Harmful Algal Blooms

June 07, 2021

An algae bloom at Cougar Reservoir produces a hazy surface.

By Adam Spencer, EWEB Communications Specialist

With parts of Lane County entering "Extreme Drought" conditions and Memorial Day weekend wrapping up with a near-record heat wave, EWEB is preparing for a hot, dry summer.

Along with wildfire mitigation programs and water conservation initiatives, EWEB will continue to monitor the McKenzie River watershed vigilantly for "Harmful Algal Blooms" (HABs)—outbreaks of toxic cyanobacteria (single-celled, blue-green algae) that thrive in warm water conditions.

Although cyanobacteria are naturally occurring and represent an important part of the food web, certain species of cyanobacteria may produce cyanotoxins, which can affect the health of humans, pets, and wildlife. Under favorable conditions, such as warm water, low flow, and elevated nutrients—especially phosphorus and nitrogen—cyanobacteria populations can rapidly increase and pose a threat to downstream drinking water sources.

As the McKenzie River is currently the sole source of drinking water for around 200,000 people in Eugene, EWEB routinely tests water in 10 locations to be able to detect and treat for the effects of HABs to make sure our water is safe to drink.

When HABs occur in the watershed, they typically start in either the Blue River Reservoir or Cougar Reservoir. These large bodies of water are both managed by the Army Corps of Engineers primarily for flood control. Once filled with winter rains and spring snowmelt, summer sunshine heats up the water, creating the conditions for cyanobacteria to reproduce rapidly.

Toxins from HABs may reach detectable levels in the McKenzie River when the Army Corps of Engineers releases water from both reservoirs while bloom events are active. Once in the McKenzie River, HABs can threaten our drinking water.

EWEB protects the community's drinking water from the effects of HABs by actively monitoring multiple locations in the watershed for cyanotoxins, starting with several testing sites downstream of the reservoirs. If toxins are detected, EWEB can treat the drinking water to remove toxins. EWEB also notifies our customers when we detect cyanobacteria toxins in significant amounts.

In fact, EWEB is certified by the Oregon Health Authority to perform our own cyanotoxin tests on-site at the Hayden Bridge Filtration Plant, allowing our team of Water Quality Specialists to analyze and respond to contamination events faster. EWEB is also unique in piloting a biofilter project that can reduce algal toxins in our drinking water by employing beneficial bacteria that consume them. The water is then disinfected again to ensure safety prior to transmitting the water to town.

EWEB's monitoring and treatment programs are designed to identify and prevent detectable levels of cyanotoxins from entering our transmission pipes below the Hayden Bridge Filtration Plant. To date, EWEB has never had to issue a single warning for a Harmful Algae Bloom affecting drinking water.

With the hot summer to come, we will increase monitoring efforts and continue to communicate our findings to our customers, as it's your right to know what's in your drinking water.

To learn more about EWEB's cyanoHAB monitoring and treatment program, including to review recent testing results, go to:

Stay Safe When Swimming

It's important to research current conditions when heading out to swim in lakes, ponds, and reservoirs during the spring and summer months to avoid locations with active HABs. The Oregon Health Authority (OHA) has an emergency email/text alert system and may post warning signs in affected areas.

As not all water bodies are monitored for HABs, swimmers and pet owners should avoid water that "looks foamy, scummy, thick like paint, pea-green, blue-green or brownish red," according to OHA.