TOLEDO, Ohio — The toxins that contaminated the drinking water supply of 400,000 people in northwest Ohio did not suddenly appear.
Water plant operators along western Lake Erie have long been worried about this very outcome as a growing number of algae blooms have turned the water into a pea soup color in recent summers, leaving behind toxins that can sicken people and kill pets.
The problems on the shallowest of the five Great Lakes brought on by farm runoff and sludge from sewage treatment plants have been building for more than a decade.
While residents around Ohio’s fourth-largest city were being told to avoid drinking tap water for a second day on Sunday, discussion began to center around how to stop the pollutants fouling the lake that supplies drinking water for 11 million people.
‘‘People are finally waking up to the fact that this is not acceptable,’’ Toledo Mayor D. Michael Collins said.
City and state officials were waiting for a new set of samples to be analyzed Sunday before determining whether the water was safe.
‘‘This is not over yet,’’ said Collins, who added that some samples have showed decreased levels of toxins.
Toledo officials warned residents not to use city water early Saturday after tests at one treatment plant showed readings for microcystin above the standard for consumption, most likely because of the algae.
Drinking the water could cause vomiting, cramps, and rashes. Health officials advised children and those with weak immune systems to avoid showering or bathing in the water.
Told not to drink, brush their teeth, or wash dishes with the water, residents descended on truckloads of bottled water delivered from across the state as the governor declared a state of emergency.
Some hospitals canceled elective surgeries and were sending surgical equipment that needed sterilization to facilities outside the water emergency, said Bryan Biggie, disaster coordinator for ProMedica hospitals in Toledo.