The line formed outside Walt Churchill's Market & Pharmacy in Perrysburg, Ohio, at the crack of dawn Saturday, before the business even opened.
Toledo-area residents, desperate for clean water, bought all the bottled water inside, market co-owner Bob Carpenter said.
Then, hearing that a water tank truck full of about 8,000 gallons had set up outside the store, more people descended on the oasis with empty jugs they could fill for a dollar a gallon.
The "water rush" came after two samples from a water treatment plant showed readings for microcystis, a toxin that is released by algal blooms.
And that scene may repeat itself Sunday morning across metropolitan Toledo, stretching across the state line into southeast Michigan.
Some 400,000 people will go to sleep Saturday not knowing whether their drinking water is safe, as test results expected Saturday night weren't completed, and advisories won't change until Sunday morning at the earliest, said Heidi Griesmer, spokesperson for the Ohio Environmental Protection Agency.
Residents have been told not to use, drink, cook with, or even boil any tap water, and those advisories will stand overnight, Griesmer said.
About two-thirds of the Toledo area population are affected by the water warning. Ohio Gov. John Kasich issued a state of emergency for Fulton, Lucas and Wood counties. And the potential contamination also affects four municipalities in Michigan, CNN affiliate WXYZ reports.
"We hope the tests come back and that we are not in the dire strait we fear we might be in," said Toledo Mayor Michael Collins. "We are erring on the side of caution."
There are no reports of anyone getting sick from the water, officials said.
Harmful Algal Blooms
When certain conditions are present, such as high nutrient or light levels, algae can reproduce rapidly, forming a dense population known as a "bloom," according to the National Oceanic and Atmospheric Administration
Toledo's drinking water comes from Lake Erie, where a harmful algae bloom that causes microcystis has been growing, according to a city spokeswoman.
Testing is crucial, because NOAA says it can't tell just from images if blooms are toxic or not.
Ingestion of the toxin can affect the liver and cause nausea, diarrhea, vomiting, and even acute liver failure, according to NOAA. But the Ohio state emergency management agency said it is safe for adults to shower and for everyone to wash their hands.
Where can people get water?
City officials said water was on the way from all over the state to the affected area, and families in need would get one free case.
The Ohio National Guard and Ohio Department of Transportation are delivering water to the area, and the Ohio Department of Rehabilitation and Correction is producing potable water at an adapted milk processing plant, Griesmer said.
People who lined up at planned water distribution sites were told to return when the water arrived.
"I don't advise you to go to there and wait for it," Mayor Collins said in a news conference, during which he urged people not to panic, and to let common sense prevail.
He said the city would tell people where to go once the free water arrived, and local media updated their websites with that information throughout the day.
"I assure you we will have water. There is no one going without water at the end of the day. I guarantee you that," he said.
Despite the plea, many people remained in line at one distribution center, according to WTOL.
A grocery store called The Andersons said when it received two truckloads of water, it limited sales to four cases per customer.
"It's one of the busiest day I've had in my 28 years," store manager John Kowalski told CNN.
Kroger said all its stores in the Toledo area ran out of water. Stores in the Columbus area, more than a two-hour drive away, were close to running out.
More bottled water is on the way to its 15 stores in the affected area, said Kroger spokeswoman Jackie Siekmann.
"As soon as the water shipments are in, they are going out the front door," she said.
Green leaf lettuce and other produce that is misted by water in Kroger stores will be thrown out as a precaution, Siekmann said.