The Rev. Jesse Jackson says Flint, Michigan, residents coping with a drinking water crisis "have been betrayed."

The civil rights leader told a crowd at a church Sunday in Flint that the full effect of the lead contamination of the city's tap water is not yet known.

He says there should be "tape around the city, because Flint is a crime scene."

The water became contaminated after Flint switched from the Detroit water system to the Flint River as a cost-cutting move. The corrosive water lacked adequate treatment and caused lead to leach from old pipes.

Jackson's comments came a day after President Barack Obama signed an emergency declaration that clears the way for federal aid.

Authorities and volunteers have already been distributing free water, filters and other supplies.