Ohio's fourth-largest city is still facing the threat of toxins contaminating water supplies along western Lake Erie even though the the tap water was declared safe, according to The Associated Press.

The algae leaving behind the dangerous toxins each summer aren't supposed to peak until September and the chances of another water emergency over the next few months will depend a lot the winds, rains and temperatures that dictate how large the algae grow and where algae blooms end up, the AP reported.

Lake Erie, the shallowest of the Great Lakes, supplies drinking water to 11 million people in Ohio, Michigan, Pennsylvania and New York along with Canada, the AP reported.

What role the algae-induced toxin played in fouling the water supply for 400,000 people in and around Toledo is being investigated, as is the city's aging water supply system and how it operates, but researchers believe winds pushed the algae right to where Toledo collects its water from the lake, according to the AP.

"To some degree, there are only certain things we can control," said Craig Butler, director of Ohio's Environmental Protection Agency, according to the AP. "What is possible is making sure systems taking water from Lake Erie are being very vigilant with the treatment process."

"When they bloom and it's right over our intake, we're at its mercy," said Ed Moore, Toledo's public utilities director, the AP reported. "This is Mother Nature we're dealing with. This was out of our control."

Water plants add a chemical called activated carbon to absorb algae before filtering the water, according to the AP. What makes combating the toxin a challenge is that there are no standards on how to handle it or rules on how often to test the water.

Toledo's mayor asked Tuesday for a voluntarily reduction in water usage until the algae season is over in September, saying it would give chemicals the city adds to the lake water more time to combat the toxins, the AP reported.

"Let's be realistic; we know it's going to intensify," said Mayor D. Michael Collins, according to the AP.

In September, one township just east of Toledo told its 2,000 residents not to drink or use the water coming from their taps, which is believed to be the first time a community has banned residents from using the water because of toxins in the lake, the AP reported.