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Detroit Lake in Detroit, Oregon, Saturday, March 18, 2017. Detroit Lake flows downstream into Salem's drinking water intake. Bradley W. Parks / OPB

For the second time in two weeks,

Salem is under a drinking water advisory

, and there’s very little the city can do about it.

Test results released Wednesday from water collected four days prior found an algae-produced toxin was present at levels deemed unsafe for certain groups to drink. It’s left city and state residents asking how it happened and wondering if it will happen elsewhere.

The toxins in the water are caused by a harmful algal bloom in Detroit Lake, a reservoir on the Santiam River that provides Salem with drinking water. These blooms sometimes cover an infected lake with a bright, turquoise scum that produces a dangerous toxin.

Despite their common name, the “blue-green algae” that cause it are more closely related to bacteria than seaweed. The microscopic, single-celled organisms are more accurately called cyanobacteria, and there are thousands of species of them. Some are harmless, some are dangerous. Like most plants and seaweeds, cyanobacteria make food from the sun via photosynthesis, which gives them their green color.

Harmful algal blooms have recently emerged as a major public health issue across the country, and even globally. In 2012, the Environmental Protection Agency conducted a survey of lakes across the U.S. They looked at more than 50,000 lakes and found that one in three tested positive for high levels of cyanotoxin.

It’s no small concern: depending on the level of contaminants, drinking tainted water can cause a variety of problems, ranging from respiratory distress to kidney issues.

A Sampling Problem

The Oregon Health Authority algae bloom advisory archive listed 12 harmful algal blooms in the state last year. But according to Rebecca Hillwig, a natural resource specialist on the Oregon Health Authority's Algae Bloom Surveillance Program, the actual numbers are much higher.

Related: OHA To Require Regular Testing For Cyanotoxins In Drinking Water

Prior to 2015, OHA and Army Corps of Engineers had money to regularly test lakes that people used for recreation and lakes that served as part of the water supply. But that money ran out. Now, lakes are only tested if there’s a visible algal bloom (and sometimes, not even then) or if a city sets aside money to pay for testing.

“That’s why it looks like there’s such a huge problem at Detroit Lake,” Hillwig said, referencing positive tests for cyanotoxins in 2007, 2015 and 2017. “Salem has the ability to do the sampling.”

Dexter Lake, a reservoir above the Eugene/Springfield area, used to regularly test positive for cyanobacteria. But when funding ran out, the Army Corps of Engineers ceased regular testing. The only agency that regularly tests lakes is the Forest Service, but “they have a lot of lakes to test, so it’s constant triage,” Hillwig said.

The situation is worse east of the Cascades. Testing doesn't really happen there, Hillwig said, and there’s no data on how common blooms are.

Right now, many locations just do an eyeball test. If the water turns pea-colored, locals might test it if they have the money. Or they might simply put up a sign saying not to use the lake. In other cases, nothing might happen. In 2017, a massive harmful algal bloom was identified in a Lake County pond, but only after 32 cattle died.

While it seems like the issue is getting worse, “we don’t have any data,” Hillwig pointed out. “There’s not enough for trends. Are they getting worse? Are we just becoming more aware? We can’t tell.”

But Hillwig is concerned that the blooms might get worse in the future, even if there isn’t enough data to track it.

“It’s likely climate change will impact how many blooms we see, the length of time that they’re in place," she said, "but it’s hard to say without funding to back it up.”

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A Growing Problem

The EPA's National Lake Assessment is the most robust study of lake health in the country. And it does show that harmful algal blooms are becoming more common. Harmful algal blooms were 8.3-9.5 percent more common in 2012 than they were in 2007, depending on the way it's measured.

In 2014, a massive algal bloom in Lake Erie contaminated the city of Toledo, Ohio's water supply. Blooms have occurred in Erie almost every year since.

There are a variety of factors contributing to this increase. Agricultural runoff from farms is a big player; the nutrients that make plants grow, like phosphorous and nitrogen, also make cyanobacteria grow. Without them, there are no blooms. But algal blooms also require warmer-than-usual water temperatures.

In many parts of the country, rising temperatures have been linked to climate change. And that may be the case in Oregon as well. The 2017 Oregon Climate Change Assessment Report says that climate change may lead to more toxic algal blooms in Oregon.

It’s impossible to say with certainty if climate change has played a role in causing the algal bloom in Detroit Lake, but Kathie Dello, associate director of the Oregon Climate Change Research Research Institute, said that May was the fourth hottest in Oregon history, as well as one of the driest.

The Right Ingredients

Even with very little data, it’s clear that Oregon’s mountain reservoirs, like Detroit Lake, are prone to algal blooms. Many of the state’s largest reservoirs tested positive regularly when that testing still happened. Reservoirs have all three ingredients necessary for a bloom: still water, warmer-than-usual water and high nutrient levels.

Related: Salem's Mayor Orders Investigation Of Cause Of Detroit Lake Algae Blooms

The nutrients can come from a number of places, not just agriculture. It could come from leaking septic tanks, or from runoff caused by changes in forest practices.

One large part of the problem could be how we use our reservoirs, Hillwig explained. Since they control the water level in the rivers below them, we drain our reservoirs in the winter.

“Less water means it’s warmer and higher in pH," she said. "Sort of this perfect storm of conditions that cyanobacteria like.”

Additionally, when the lake is dry, sediment and nutrients accumulate in the bottom. And when Spring comes and water is allowed back in the reservoir, it brings in fresh nutrients and stirs any accumulated on the bottom back up into the water column.

Salem Mayor Chuck Bennett has ordered an investigation into the cause of Detroit’s algal bloom, but Hillwig isn’t sure they’ll turn anything up. There are just too many factors.

It also isn't clear why this year toxins from the algae made it into the water supply. This years' bloom doesn't seem larger than the previous years' and water in the town of Stayton, which draws its water just two miles further downstream than Santiam does, is testing clean.

Beyond Salem

Many cities in Oregon draw their water from similar sources to Salem: locations downstream from mountain reservoirs. And many of those reservoirs have had harmful algal blooms in the past. Their federally required yearly water standards did not require testing for cyanobacteria. The only bacteria they had to test for were ‘fecal coliforms,' which can indicate the presence of feces, and related disease-causing bacteria and viruses in the water.

If these toxins ever did make it into municipal drinking water in the past, no one noticed. Concerned that algal blooms may be becoming more common, the Oregon Health Authority has issued new rules requiring cities to routinely test major water sources for contaminants. If those sources are contaminated, they will then test raw water going into the city systems, and if toxin levels are too high in those systems, they will test the drinking water.

The Future

As of Wednesday, it was still unsafe for infants, children, pregnant or nursing women, the elderly and at-risk populations like those with kidney problems to drink the water in Salem. It was also unsafe for pets.

And that might not change any time soon.

Salem’s water treatment system can’t remove cyanotoxins from the water. In fact, very few water treatment facilities in the country can. There are possible updates to the water treatment system that cities with water prone to algal blooms have used, but they are expensive. Salem isn’t ruling it out.

“We’re definitely looking at what we need to do in the future,” said Salem city spokesperson Kenny Larson, “but for now we’re just focused on the short term, of getting water safe for all residents.”

Unfortunately, all the city can do is dilute the water so toxin levels are below the EPA-recommended cutoff, and wait.