UPDATE: The advisory's been lifted.

SALEM -- Every 20 minutes or so, a few cars pull into Woodmansee Park and their drivers unload plastic water bottles, old Pepsi bottles or washed out milk jugs -- anything they can fill with clean drinking water.

Salem is in Day 5 of a water advisory that cautions vulnerable people and pets from drinking tap water. The first cyanotoxin scare for the city's drinking supply comes after years of algae blooms have spread the toxins off the coast and in major waterways.

Meanwhile, 30 miles north in Wilsonville and nearby Sherwood, residents were notified Friday that traces of cyanotoxins were found in city water drawn from the Willamette River. City officials will find out Monday whether they need to issue a similar warning.

"We're being abundantly cautious here and providing information that allows our community members to make an informed decision," said Wilsonville City Manager Bryan Cosgrove.

The slow pace Friday at Woodmansee marks a stark contrast to the rush on bottled water at Salem-area grocery stores in first hours after the advisory was issued late Tuesday.

Salem officials have since apologized for panicking residents. The response also caught the attention of state lawmakers.

At Woodmansee, the Oregon National Guard filled containers with a spigot attached to a 2,000-gallon tanker truck. Residents were only supposed to take 5 gallons at a time.

Sgt. Ronald Eckert said their "hippo," as the trucks are affectionately called, is almost empty. Since 9:30 p.m. Thursday, volunteers and Guard members have distributed 1,600 gallons to about 800 people.

Eckert said Woodmansee and three other sites will dispense water round-the-clock until city officials lift the advisory.

That relief could come this weekend.

Salem needs two days of clean test results before it can lift a water advisory that caused some residents panic. Lacey Goeres-Priest, a city water quality supervisor, said Friday that the latest round of tests came back at an acceptable level. Though there's no guarantee, because toxin levels can wax and wane, water treatment staff say the trend line is headed in the right direction.

Currently, the vast majority of residents in the Salem area are encouraged to keep drinking the tap water. The advisory applies only to children younger than 6; the elderly; people with compromised immune systems; nursing and pregnant women; and pets. The affected locales are Salem, Turner, the Suburban East Salem Water District and Orchard Heights Water Association.

This week's advisory marks the state's first cyanotoxin warnings for tap water.

Algae blooms have become more common in Detroit Lake, where much of Salem's drinking water comes from, over the last decade. It is a relatively new problem to the Pacific Northwest, so officials have been sending samples by rush order from four water monitoring sites to a laboratory in Ohio. The toxin is more often found in the Midwest.

But the danger of cyanotoxins is still an emerging problem in the country, said Dave Emme, who manages the Oregon Health Authority's drinking water program. The U.S. Environmental Protection Agency doesn't yet regulate cyanotoxins, which can take years of testing and analysis.

So when Salem city officials contacted the EPA and Oregon Health Authority to consult about their tap water, the three agencies had to figure out their protocol on the fly.

Healthy people older than 6 can drink large amounts of water with the low level of toxins found. But even those who fall into the advisory's net have 10 days of drinking infected water before they risk getting sick.

Emme said that the level that triggers an advisory for vulnerable people comes with a lot of padding -- so that even if someone drinks the water, they probably won't get sick.

Those who are susceptible to cyanotoxins could experience nausea, diarrhea or vomiting. The two strains in Salem's water could harm the liver or kidneys of people who already are medically fragile.

The city has taken considerable heat for waiting four days before notifying the public of the cyanotoxins, and officials have said they regret that. But they also said it wasn't a tactic to hide information or stall a backlash.

Instead, they were complying with the EPA's guidelines.

At a news conference Friday, Salem City Manager Steve Powers expressed dismay about the city's initial outreach strategy.

"I regret that the initial water advisory and the city's communication about the water advisory had the widespread impact that have occurred for the past 60 hours," he said. "We were trying to achieve the exact opposite -- maintaining confidence in our water system and our water."

Since the toxins were detected, Goeres-Priest said her staff increased the number of locations they monitor the water -- including at its source in the North Santiam River, the reservoir of Detroit Lake and within the treatment process.

When the advisory was extended into Thursday, Gov. Kate Brown issued an emergency declaration that allowed her to tap the Oregon Military Department to distribute clean water to area residents. Though there's been a steady flow of residents stopping by to fill their containers, the initial run on water has largely abated.

Peter Fernandez, who directs the Public Works Department, outlined several steps he and the city manager are considering to prevent future cyanotoxin scares.

The treatment plant could close its gates to stop infected water from entering the plant, though that is more difficult to do in the summer when water usage is high.

The treatment plant staff already is experimenting with mixing groundwater reserves with river water to dilute the toxin levels. They could also add more chlorine or use roughing filters before the city's usual slow sand filter.

Because the Detroit Reservoir is a reliably clean source of water, the city uses a filtration system that is uncommon in the U.S. Water is slowly passed through a fine layer of sand to let the natural processes take out bacteria.

Fernandez said the city could expand its groundwater reserves for the future, which would require other filtration processes.

Oregon Senate President Peter Courtney plans to look at how to better prepare as a state.

"Whether it's the next algae bloom or a devastating Cascadia earthquake, we have to be better prepared," Courtney said. "We need timely access to critical information. We have to communicate better. We have to do a better job of meeting the needs of our people. It's been clear this week that our emergency response infrastructure is not what it needs to be."

He said he wants to hold a legislative hearing to review the Salem water case to discuss how city and state agencies can quicken the pace of water testing, distribute safe water better and communicate emergencies better with the public while avoiding causing hysteria.

-- Molly Harbarger

mharbarger@oregonian.com

503-294-5923

@MollyHarbarger

-- Corlyn Vorhees