Health authorities tested water for toxins in Toledo, Ohio, on Sunday as some 400,000 people remained without safe drinking water for a second day following the discovery of high toxin levels from algae on Lake Erie.

Toledo Mayor D. Michael Collins said some sampling showed decreased toxin levels but results from further tests would not be known until later in the day. The city is waiting on water samples being analyzed at Environmental Protection Agency labs in Cincinnati.

"All I can tell you is that everything is trending in a very positive direction," Collins told reporters, but he added that he could not predict when water would be safe to drink.

Toledo Water Problems

Isaac Miles, of Toledo, Ohio, sells water he purchased in Michigan as people in both states scrambled for bottled water following the ban on drinking tap water. (Andy Morrison/The Blade/Associated Press)

About 500,000 people get water from the contaminated source but about 100,000 residents of some communities have backup water supply systems, said city of Toledo spokeswoman Lisa Ward.

Toledo Public Utilities Director Edward Moore said a plan is in place to swiftly flush the system of contaminated water once the water supply is deemed safe. Residents will be advised how long to run water in their homes to clear pipes of contaminated water.

Health officials sent samples to several laboratories after finding Lake Erie, which provides the bulk of the area's drinking water, may have been affected by a "harmful algal bloom," Ohio Environmental Protection Agency spokeswoman Heidi Griesmer said.

Ohio Governor John Kasich declared a state of emergency on Saturday for the state's fourth-largest city and surrounding counties. The city and other agencies have established sites where bottled water is being distributed free to the public.

"Everybody needs to stay cool and calm," Kasich told a news conference on Sunday. "We're going to learn from this and make improvements."

A spokeswoman for Ontario's Ministry of the Environment and Climate Change said the blue-green algae bloom has not moved into the province's waters and is not affecting municipal drinking water intakes in the lake.

"Ontario's drinking water is among the best protected and tested in North America," Kate Jordan told CBC News. "The local treatment plants in Chatham-Kent and Elgin regularly test for microcystins and none have been detected."

Residents seek safe water

Many residents drove to other states in search of fresh water as stores rapidly sold out of bottled water.

Jeff Hauter of Toledo drove to a Walmart in suburban Detroit where he bought 18 gallons and four cases of water. He said he ran into others from the Toledo area loading up their vehicles.

Algal blooms in Lake Erie are fairly common, typically in the summer, state emergency operations spokesman Chris Abbruzzese said. Potentially dangerous algal blooms, or rapid increases in algae levels, are caused by high amounts of nitrogen and phosphorous.

2011 Lake Erie Algae Bloom

University of Michigan researchers and their colleagues predict a significant bloom of toxic blue-green algae in Lake Erie late this summer. (National Oceanic Service)

Those nutrients can come from runoff of excessively fertilized fields and lawns or from malfunctioning septic systems or livestock pens, city officials said.

Drinking the contaminated water can affect the liver and cause diarrhea, nausea, numbness or dizziness, officials said. Boiling will not destroy the toxins.

The water should not be used for drinking, making infant formula or ice, brushing teeth or preparing food, the governor's office said. It also should not be given to pets, but hand washing is safe and adults can shower in it, officials said.

In response to the Toledo crisis, Chicago began additional precautionary testing on Lake Michigan water, a city spokeswoman said.

With files from CBC News