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

Snyder said in January he had just learned about the rise in Legionnaires cases. However, emails obtained by the liberal group Progress Michigan and released to reporters on Thursday show Snyder’s principal adviser, Harvey Hollins, was made aware of the outbreak and a possible link to the use of Flint River water last March.

A spokesman for Snyder could not be reached for comment.

“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 state department of environmental quality, 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, 2016, announced the spike in the disease resulting in 10 deaths possibly linked to the water crisis.

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 blood samples taken from children. 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. The mist may come from air-conditioning units for large buildings, hot tubs or showers.

On Wednesday at a hearing in Washington, U.S. lawmakers criticized environmental officials for not acting sooner when they saw drinking water in Flint was polluted with dangerously high lead levels. Several Democratic lawmakers on Thursday invited Snyder to Washington to testify on the Flint water crisis on Feb. 10.

Senate Democrats also teamed up with Republicans to block a wide-ranging U.S. energy bill in a fight over aid to help Flint cope with the crisis.

(Reporting by Mary Wisniewski in Chicago and Ben Klayman in Detroit; Editing by Andrew Hay)