Transcript for How Flint, Michigan's Contaminated Water Was Discovered
It's a public health crisis of massive proportions. Lead in the water supply in Flint, Michigan. People breaking out in rashes, losing hair. The doctor who sounded the alarm was ignored. But not anymore. ABC's Alex Perez is following the investigation in Flint tonight. Three, two, one -- Reporter: It was supposed to be a moment of triumph. Cheers erupted as the then-mayor of Flint, Michigan, officially turned off the water feed from Detroit. Here's to Flint! Hear, hear! Reporter: And began pulling its supply from the local Flint river. Little did they know that this cost-cutting move would have devastating consequences. Cheaper than Detroit but about at what cost? Health, people dropping over dead, getting sick? Clean water! Reporter: Now almost two years later, Flint is in a state of federal emergency. Our children should not have to be worried about the water that they're drinking in American cities. That's not something that we should accept. Reporter: President Obama releasing $80 million in aid to Michigan to help Flint repair its water infrastructure. As national guards continue to cart in thousands of bottles of water and filters. But on that day back in April 2014, as the mayor pressed the button, no one knew what they had put into action. Just weeks after the complaints began pouring in about discolored and foul-smelling water running from the taps. Mysterious ailments. This 2-year-old would become the face of this public crisis, suffering severe rashes, hair loss. At the time his mother had no idea what it was. She was not alone. My son Jordan, he's been in the E.R. Twice, early summertime with rash all over his body from the water. Today we went in for high fever, cramping, sore throat -- Reporter: Mothers like brandy luck were starting to turn up at emergency rooms all over Flint. Jaden was seen today for a severely sore throat, very swollen, very red. Reporter: Long-time residents Jacob and his wife had taken to bathing their young children with bottled water. You hear of all these legionnaires disease or the dermatitis. All these different things that are happening more and more frequently. Nobody's accountable. No one's been prosecuted. No one's served a penalty for this. Except for the people of the city of Flint. Reporter: For almost two years complaints from the city of 100,000 residents went unanswered. But independent test results were beginning to provide a chilling answer. High levels of the lead in the water. The lead is an irreversible neuro toxin. Once it is in your body the damage is done. Reporter: This doctor, director of pediatrics at hurley medical center in Flint, was one of the first to sound the alarm. What we noticed was that after the water switch, the percentage of children with elevated blood lead levels doubled in the city of Flint. In some neighborhoods it tripled. Reporter: When she released her findings in September 2015 -- Right away we were attacked. We were told we were wrong, that we were unfortunate researchers, that we were causing hysteria. Reporter: Two weeks later officials could no longer ignore the signs and officially declared the water unsafe. This week the fallout. As over 270 pages of internal e-mails and documents came to light. It's a damning look into how officials ignored blatant warning signs. Some of those signs were uncovered by this man, EPA investigator Miguel del toro. I never imagined this would happen in the first place. Reporter: He was one of the first to warn about lead in the water after resident Leann Walters called in a complaint in early 2015. Del toro went to her house to test the water. What she found was extremely high levels of lead in the tap water. Water that he said was causing Walters' children's hair to fall out in clumps. I think that if it weren't for Leann, this may have gone a lot longer. Reporter: After talking to the state department of environmental quality del toro made another stunning discovery. The river water being fed into the taps was not being treated with anti-corrosion agent, as required by law. Inconceivable that you would allow a system with lead service lines, a large system, not to have the treatment in place. Reporter: In the spring of 2015, del toro warned the agency that the state was understating the lead levels in the city's water. Writing in a memo, staffers have essentially downplayed or ignored warning signs. And that the whole town may have much higher lead levels than the compliance results indicated. You give them that warning, seems like they blew you off. Did they not know what they're doing? I don't know what their decision process was on this. Reporter: Internal memos show state officials dismissed multiple warnings, spending months denying the lead contamination until October of last year. Sad to see what's happened there. Shouldn't have happened? Shouldn't have happened. Reporter: When Dan wine, director of the department of environmental quality, wrote in an e-mail, I believe now we've made a mistake, corrosion control should have been required from the beginning. Admission met with public anger in a city where more than 40% live below the poverty line. Residents are asking if they're being left behind. If this was a highly generated economy and it was booming here, then yeah, it wouldn't have made it past three months. Reporter: Flint's water supply has since reverted back to Detroit's lake Huron but the damage has been done. An independent task force conducted a review of the state's handling of the water crisis and found the deq's response to the public to be "One of aggressive dismissal, belittlement, and attempts to discredit these efforts." The head of the EPA's regional office in Chicago which covers Michigan has resigned after governor Rick Snyder officially apologized to the residents of Flint. I say tonight as I have before, I am sorry and I will fix it. Reporter: The apology coming just hours after attorneys filed a class action lawsuit against the governor and state and city officials. Dr. Hannah says apologies don't mean that much to a mother wondering what will happen to her child. She's traumatized about the cons consequences of lead. But they're also traumatized about what they've been through the last two years. An entire betrayal of governmental agencies. Reporter: Or to a city that will have to live with the consequences. You expect when you turn on your water, you expect it to be drinkable. And you've been told for almost two years that it's safe. So there's significant trauma in the community. We are definitely trying to instill hope. Reporter: For "Nightline," I'm Alex Peres, Flint, Michigan.
This transcript has been automatically generated and may not be 100% accurate.