A toxin found in the Toledo, Ohio water system left residents coping with the second day of a city tap water ban, after the mayor said the water was not safe to use, reports the New York Times.

Mayor D. Michael Collins said Sunday morning he was not ready to lift a ban on using City of Toledo water for brushing teeth, drinking, or preparing food. The water quality appeared to be improving, but the authorities needed to examine further test results to determine whether the water was safe, said the mayor.

“This is not over yet,” said Collins. “We do need to get the rest of the results.”

Mayor Collins declined to provide details on recent testing or say when the ban might end. “All I can tell you is everything is trending in a very positive direction,” said Collins to reporters at a news conference.

Testing at a city water treatment plant found unsafe levels of microcystin, a toxin that can cause diarrhea, vomiting or abnormal liver function, said city officials. The city issued a notice on Saturday saying the water was unsafe for use.

The City of Toledo water system serves about 500,000 people in the region and the ban applies to all customers. Ohio National Guard members were delivering water and food. Several water distribution centers have been set up at fire stations and high schools.

A “harmful algal bloom” in Lake Erie may have contaminated the city water supply, said city officials. Runoff from over-fertilized fields, malfunctioning septic systems or livestock pens often cause the blooms, said the water notice.

Toledo is on the southwest edge of Lake Erie near the Michigan border. Algae blooms that appear on the lake each summer have caused concern in the region for years. Blooms have been blamed for reducing fish populations, polluting beaches and hurting tourism.

Ohio Gov. John R. Kasich declared a state of emergency in the area on Saturday. The governor planned to meet with Mayor Collins on Sunday afternoon to discuss water test results and to “work through what needs to be done in terms of bringing this horrendous, negative experience to a positive end,” said the mayor.