John Bacon

USA TODAY

A toxin discovered in a northwestern Ohio treatment plant left 500,000 people scrambling for drinking water for a second day Sunday.

Toledo Mayor D. Michael Collins said preliminary testing showed toxin levels were improving at the city's plant, but he said officials were waiting for federal officials to analyze more samples before determining if the water is safe to drink.

"All of the results continue to improve, which gives us hope," Collins said Sunday. "But this is not over yet."

Results of the latest tests, expected to be announced Sunday night, were delayed until after 1 a.m., The Blade of Toledo reported. "We're doing new testing," the mayor told the newspaper.

Residents of Toledo, its suburbs and small areas of southeastern Michigan began lining up for water Saturday after news of the contamination surfaced. Ohio Gov. John Kasich declared a state of emergency for Lucas, Wood and Fulton counties and deployed the National Guard to make water available to the area.

The National Guard had produced 33,000 gallons of drinkable water by Sunday morning, and an additional 15,000 gallons had been delivered in collapsible containers.

The water problem was complicated because boiling the water, a common tool to combat contamination, only serves to make the toxin more concentrated, officials said.

Collins blamed the contamination on algae in Lake Erie, the city's main water supply. Once the tap water is ruled safe, he said, officials will try to figure out how to keep the problem from happening again.

"Once we clear this problem up, that is not going to eliminate the algae problem in the western basin of Lake Erie, that is not going to eliminate the agricultural runoff, that is not going to eliminate mega-farming," Collins said, "That is where we have to go. It's not simply looking at the (water treatment) system."

News of the contaminated water touched off a shopping frenzy at stores for bottled water and bags of ice. Shelves were emptied of bottles and other water supplies as residents prepared for the worst. Stores in cities up to 50 miles away were reporting shortages of bottled water.

The city opened a half-dozen bring-you-own-container water distribution sites. Fire stations were also helping out. Families dragging coolers or lugging jugs, bottles and even cookie jars topped them off with well water funneled out of pickup trucks.

Tyshanta DeLoney of Toledo filled up a big plastic container after spending much of the day searching for water. "That was a blessing," she said.

"The good news is the community has really and truly risen to the occasion," Collins said. "Vendors have been over-the-top great, just giving water to those who are in need. God bless them."

The Toledo Zoo said it was using its own water reserves for the animals and that flamingos were the only animals taken off exhibit Sunday as a precaution.

In Michigan, Gov. Rick Snyder said Sunday that state agencies were ready to help the 11,000 households in southeastern Michigan that remain under a water advisory. Monroe County has established stations for distributing water.

The scramble for drinking water began after chemists testing water at Toledo's Collins Park Water Treatment Plant found two sample readings for microcystin in excess of the one-microgram-per-liter standard for consumption. The Federal Emergency Management Agency estimated that 500,000 people were placed under a "do not drink or boil water" advisory.

Officials said the water is not safe for drinking or cooking but healthy adults could still use it for bathing. They warned children not to bathe or swim in it because they might drink the water accidentally. Symptoms include nausea, vomiting, diarrhea and upset stomach.

Operators of water plants all along Lake Erie, which supplies drinking water for 11 million people, have been concerned over the past few years about toxins fouling their supplies. Last year, about 2,000 residents of nearby Carroll Township were prohibited from drinking water from their taps for a few days because of toxins linked to Lake Erie algae.

Most water treatment plants along the lake's western shoreline treat their water to combat the algae. Toledo spent about $4 million last year on chemicals to treat its water.

Contributing: Rick Jervis, William M. Welch, USA TODAY; Christina Hall, Detroit Free Press; Associated Press