Though dawn was still hours away, the Smith family was awake — and scared. Alicia Smith, a mother of three, had received an early-morning alert about local drinking water.

She began calling friends and relatives to spread the news, and by 7 a.m., daughter Alexis was knocking on neighbors’ doors to get the word out.

It was Aug. 2, 2014, and the Smith family and 500,000 other residents in the Toledo, Ohio, region had awakened to a public health emergency. The local tap water was toxic. And boiling to purify only increased toxicity. With so many health questions still unanswered and limited bottled water available, confusion swept greater Toledo.

The three-day water prohibition was caused by a toxic algae bloom in western Lake Erie, the source of Toledo’s drinking water. And though no illnesses were confirmed by officials, the crisis highlighted the dangers of harmful algae to public health.

In recent years, hundreds of U.S. ponds, lakes and rivers have tested positive for algae toxins, according to a data analysis of federal and state records by the Environmental Working Group. Sixty-eight percent of people in the U.S. get their drinking water from surface water, according to the U.S. Environmental Protection Agency.

Continue reading this story from the October 2019 issue of The Nation's Health.