Flint, MichiganThe Flint River scribbles 142 miles through mid-Michigan, and a noticeable change occurs as it flows southwest into the city of Flint. Concrete slopes capped with wire fences flank the water. Occasional graffiti or a weedy bush break the monotony of such barren shores. So do decaying bridge piers protruding from the center of the river like the sails of submarines much too large for the modest waterway.

Another stark transformation happens in the few seconds required to paddle beneath the Sunset Drive bridge. Gray stone ceases and a leafy, tree-shrouded corridor unfolds.

Looking back five years, the same magnitude of change happened on April 25, 2014, when smiling city officials raised glasses of water to toast a switch that