Mexico City has treated its rivers badly: They tend to be paved over and filled with sewage. But Elías Cattan, a green building leader in Mexico City, wants to turn one of these f*cked-under resources back into a healthy, flowing river. Under Cattan’s guidance, the trash-clogged Río Piedad would become a viable waterway with a park on its banks and a transportation infrastructure dominated by walking, biking, and mass transit.

Just give him two years and $1 billion.

The city government does not share Cattan's enthusiasm and is more inclined to target less toxic and more easily mended rivers. (Río Piedad is pretty far gone — its name even means “Pity River,” as if the garbage and concrete and feces weren’t pathos enough.) And $1 billion might be too low an estimate for the work it would take to clean the river of sewage. But as Mexico City Minister of the Environment Martha Delgado understates, “The truth is that rescuing rivers is a really good idea.”

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