(Reuters) - Emails between high-ranking Michigan state officials show they knew about an uptick in Legionnaires’ disease and it could be linked to problems with Flint water long before Governor Rick Snyder said he got information on the outbreak.

The front of the Flint Water Plant is seen in Flint, Michigan January 13, 2016. REUTERS/Rebecca Cook

A spokesman for Snyder rejected the report by the liberal group Progress Michigan on Thursday. Emails obtained by the group show Snyder’s principal aide, Harvey Hollins, was made aware of the outbreak and a possible link to the use of Flint River water last March.

Snyder said in January he had just learned about the rise in Legionnaires cases.

“Are we to believe that a top staffer with years of experience would not inform Governor Snyder of a possibly deadly situation?” Progress Michigan Executive Director Lonnie Scott said in a statement.

The group cited an email from March 13, 2015, that showed Hollins and Dan Wyant, the former head of the Department of Environmental Quality (DEQ), were aware of the increase in Legionnaires’ disease in Genesee County, where Flint is located, and that a county health official was attributing the cases to the Flint River.

State officials on Jan. 13 announced the spike in the disease resulting in 10 deaths possibly linked to the water crisis.

In rejecting the group’s claims, a spokesman for Snyder said that the DEQ emails called attributing the link to problems with Flint water “beyond irresponsible.”

Hollins asked the department to investigate and if the concerns were credible it was to tell Snyder, the spokesman said in an email.

“The issue was not brought to the Governor’s attention until January of this year,” he said.

Flint, a city near Detroit, was under the control of a state-appointed emergency manager when it switched the source of its tap water from Detroit’s system to the Flint River in April

2014.

The city switched back last October after tests found high levels of lead in children’s blood samples. The more corrosive water from the river leached more lead from the city pipes than Detroit water did. Lead is a toxic agent that can damage the nervous system.

Legionnaires is a type of pneumonia caused by inhaling mist infected with the bacteria Legionella..

Several Democratic lawmakers on Thursday invited Snyder to Washington to testify on the Flint water crisis on Feb. 10.