Michigan's health chief is one of five officials charged with involuntary manslaughter in connection with the Flint water crisis.
A protester calling for clean water in Flint, Michigan. Photo: AFP
Nick Lyon and the others are accused of failing to alert the public to an outbreak of Legionnaires' disease.
However, the state governor backed Mr Lyon, calling him a "strong leader".
The outbreak involved about 100 cases and led to 12 deaths, and was thought to have been linked to poor water quality in the city of Flint in 2014-15.
Thousands of residents were also found to have drunk water poisoned with lead.
Michigan Attorney General Bill Schuette brought the charge of involuntary manslaughter against Mr Lyon, as well as Michigan water chiefs Liane Shekter-Smith and Stephen Busch, and Flint water managers Darnell Earley and Howard Croft.
Michigan's chief medical executive, Dr Eden Wells, is also facing a charge of obstruction of justice and lying to a police officer. She is alleged to have "attempted to withhold funding for programmes designed to help the victims of the crisis, and then lied to an investigator about material facts related to the investigation".
In a statement, Michigan Governor Rick Snyder said he had "full faith and confidence" in Mr Lyon and Dr Wells and that they would remain in their posts.
The charges relate to the death of 85-year-old Robert Skidmore from Legionnaires' disease in December 2015. The attorney general's office said "the charges allege failure to notify and lack of action to stop the outbreak allowed the disease to continue its spread through Flint's water system".
Mr Lyon is alleged to have known for nearly a year of the deadly outbreak and had "deliberately failed to inform the public" which resulted in Mr Skidmore's death.
The health chief is also accused of "repeatedly attempting to prevent an independent researcher from looking into the cause of the outbreak".
The other four are already facing other, lesser, charges in connection to the water crisis. If found guilty of involuntary manslaughter, the officials could face up to 15 years in prison.
Some experts believe the Legionnaires' outbreak in 2014-15 was linked to the water problems that hit Flint that same year, after the city switched its water supply.
The water from the Flint River, from where it began drawing its supply, was more corrosive than its previous source and lead began leaching from the pipes.
Nearly 100,000 residents of the poor, mostly black city, were exposed to high levels of lead, and the ensuing outcry became as much about failed governance and accountability as clean water and concerns about health.
More than a dozen people have now been charged since Attorney General Schuette opened an investigation into the crisis in January 2016.
- BBC