Prosecutors have decided to drop all criminal charges related to the Flint water crisis — and must now start the entire investigation over again.

Eight people had been charged for their alleged involvement, including former Michigan health department director Nick Lyon, who was accused of turning a blind eye to the scandal for nearly a year, resulting in the death of at least one person.

His lawyer called Thursday’s move by prosecutors “fantastic” — saying his client felt “vindicated.”

Lyon had been charged with involuntary manslaughter and was ordered to stand trial.

He allegedly found out about the Legionnaires’ outbreak unfolding in Flint in January 2015, but failed to alert the public in a timely manner, according to his charging papers.

At least 12 deaths were later linked to the area’s contaminated drinking water.

Michigan’s chief medical officer, Dr. Eden Wells, was also spared Thursday after being hit with involuntary manslaughter charges, lying to a special police agent and obstruction of justice.

The Department of Attorney General said in a press release that the decision to dismiss all charges was “not a determination of any defendant’s criminal responsibility” but rather stems from concerns that investigators had with the way the probe was handled by the former Office of Special Counsel.

“We are not precluded from refiling charges against the defendants listed below or adding new charges and additional defendants,” said Solicitor General Fadwa Hammoud and Wayne County Prosecutor Kym L. Worthy in a joint statement. “We understand this decision will not bring immediate remedy or relief to the citizens of Flint, who remain victims of one of the worst man-made environmental disasters in United States history. However, we recognize the only acceptable remedy is the vigorous pursuit of justice, which demands an uncompromising investigation of the Flint Water Crisis and professional prosecution of all those criminally culpable.”

Michigan Attorney General Dana Nessel called on the public to remain patient, and not give up hope.

“I want to remind the people of Flint that justice delayed is not always justice denied,” Nessel said in a statement. “A fearless and dedicated team of career prosecutors and investigators are hard at work to ensure those who harmed you are held accountable.”

With Post wires