Toxins possibly from algae on Lake Erie have fouled the water supply of Toledo, the state’s fourth-largest city, on Saturday, forcing officials to issue warnings not to drink the water.

Toledo issued the warning just after midnight after tests at one treatment plant showed two sample readings for microsystin above the standard for consumption.

The governor declared a state of emergency as worried residents descended on stores to buy bottled water.

The city advised about 400,000 residents in Toledo, most of its suburbs and a few areas in southeastern Michigan not to brush their teeth with or boil the water because as it would increase the toxin’s concentration. The mayor also warned that children should not shower or bathe in the water and that it shouldn’t be given to pets.

Gov. John Kasich said it was too early to say how long the advisory will last, or what caused toxins to spike suddenly in the drinking water.

The state agencies worked to bring water and other supplies to areas around Toledo while also assisting hospitals and other affected businesses.

Kasich’s emergency order allowed the state to begin bringing water into the Toledo area. Large containers were being filled with water at a prison near Columbus and trucked about 130 miles north to Toledo.

The state also asked major grocery chains to divert as much water as they can to northwest Ohio. As truckloads of water came in from across the state, Toledo leaders set up distribution centers at schools around the city, limiting families to one case of bottled water. Some stores were receiving new shipments of water and putting limits on how much people can buy. The Red Cross was helping distribute water to home-bound residents.

Some neighboring communities that aren’t connected to Toledo’s water system were offering their water to people who brought their own bottles and containers.

Algae blooms during the summer have become more frequent around the western end of Lake Erie, the shallowest of the five Great Lakes. The algae growth is fed by phosphorous mainly from farm fertilizer runoff and sewage treatment plants, leaving behind toxins that can kill animals and sicken humans.