A water treatment plant manager in Flint, Mich., told state environmental officials that the city wasn’t prepared to monitor water quality days before it began using water from the Flint River, a move that ultimately resulted in widespread lead contamination, according to recently released state emails.

Michael Glasgow, laboratory and water quality supervisor for Flint’s water treatment plant, told an environmental quality analyst with the Michigan Department of Environmental Quality in an April 17, 2014, email that he needed...