The city of Salem began regular, voluntary water sample testing at several locations in early May, when algae blooms started appearing in Detroit Lake.

The lake, which flows downstream and into the city's drinking water intake, was free of toxins. That was until test samples taken last week and received Saturday revealed low levels of cyanotoxins caused by the blooms.

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The city issued a drinking water advisory for the city's vulnerable populations Tuesday evening.

"There was non-detect for a very long time — pretty much the entire month," said Gregory Walsh, emergency manager for the city of Salem. "Based on the numbers from one day to the next day, there was a very large change in toxins."

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

Agencies say they're acting out of an abundance of caution as they wait for new test results that are expected to arrive Thursday. That includes the Oregon Health Authority, which is working closely with the city and is now recommending Salem-area hospitals refrain from using tap water.

"In those hospital settings, until we get further results back, we recommend they do not expose any of their patients to procedures using tap water," said Dr. Katrina Hedberg, health officer and state epidemiologist with the Oregon Public Health Division. "This would include cleaning wounds that are post-surgical, bathing, those kinds of things, that they wait until we get results back."

That also includes elective surgeries.

"I do want to stress that we're primarily being precautionary," Hedberg said. "The levels that have been found, while they have been detectable, are below the threshold that we would normally have a concern for the vast majority of the population."

Walsh says the city decided to alert area residents when it received the positive results for toxins. People in and around Marion County were thrown into confusion Tuesday evening, after the Oregon Office of Emergency Management (OEM) sent a vague text message alert in response to the water contamination.

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“Civil Emergency in this area until 1128PM,” the alert read. “Prepare for action.”

The opacity of the message led bewildered citizens to call emergency dispatchers, prompting statements from a number of law enforcement agencies that no emergency existed.

On Wednesday, OEM said the text message was sent in error. The agency was attempting to use the federal Wireless Emergency Alerts system for the first time since it became available in 2013, according to spokesman Cory Grogan. Due to what Grogan called “user error” the OEM sent an unhelpful default message out at around 8:30 p.m.

“When we’re talking about these messages they need to be concise and specific,” Grogan said. “It is really important.”

OEM realized the error and sent out a more specific message about the water troubles roughly a half-hour later. And the agency said it’s figured out what went wrong with the text alert, but Grogan said they are unable to test the alert system before use.

“It’s not an excuse,” he said. “It is an issue though.”

The wireless emergency alerts system, or WEA, is used by agencies around the country to alert citizens to everything from missing children to minor public safety threats. The city of Portland, for instance, has used the system to warn people not to travel in icy conditions.

Walsh says the city is working on a public-private partnership to activate a water distribution network if needed, depending on the results of incoming water samples. Extra water shipments to area stores are coming as early as Wednesday night.

Lacey Goeres-Priest, Salem’s water quality supervisor, says the city made modifications to the water treatment process throughout last week to prepare for what was coming downstream.

“This included receiving water from the city of Keizer … So we’ve been getting groundwater supplied to us,” Goeres-Priest said. “We also activated our aquifer storage and recovery well system in South Salem to help introduce that water into the system.”

Goeres-Priest says the city is not required under the Safe Drinking Water Act to test for cyanotoxins in its water.

"The algal blooms can change within hours [and] can go from a high level to a complete non-detect," Walsh said.

"What's nice is that we'll have a couple of days of data, so if it's all clear it provides a really easy answer to say all clear. If not, then we can continue the advisory until we have all clear results."