Flint switched it's water supply to a river in 2014 and the river or old pipes had lead in it. Sometime after this problem was identified Flint switched it's water supply back to Detroit city.
A bunch of leftists like Michael Moore, Hill Rod and that Bern weirdo are attempting to blame the governor for this problem and demanding he resign. Some of the wackiest leftists (Moore included) are demanding he be arrested and charged with crimes like assault and conspiracy (not sure what crime he allegedly conspired to commit, that wasn't reported). They apparently think the governor intentionally poisoned these people. His motive is, of course, unclear.
I don't know if this is really a State issue. I think the allegation is it took too long for the city to switch back to the original water supply, and the governor had something to do with that. I'm sure one of the resident leftists can explain why this is a huge cover up, racist and a bunch of other sinister stuff since the governor is a pub, I think.