Slate: Bill de Blasio has plans to part the East River—and expects New Yorkers to follow him 500 feet into the estuary, to a new land that will protect downtown from the sea.

On Thursday, New York’s mayor reiterated the city’s intent to preserve its core by reclaiming a slice of New York Harbor between the Brooklyn Bridge and the southern tip of Manhattan Island, planting as many as 20 new New York blocks into the silt to keep the rising Atlantic Ocean at arm’s length.

On the one hand, the East River extension is a gargantuan, once-in-a-lifetime endeavor that would transform New York City, at a cost the mayor pegged at $10 billion. On the other, it’s just the latest step in Manhattan’s long march into the harbor, which began with blocks of muddy “water lots” sold to enterprising colonists and culminated with the 1970s construction of Battery Park City on 92 acres of landfill. Read More>>