New York City's swirling, tide- and current-tossed East River, which runs from New York Harbor to Long Island Sound (and is therefore not a river in the usual sense and more of a salt-water connection left over from the last Ice Age) separates Manhattan from Brooklyn and Queens, and further east separates the Bronx from Queens.
It is spanned by eight bridges and has 13 tunnels, all but one of the tunnels (the Queens-Midtown Tunnel) for rail. A friend took this photo on Saturday, with the majestic Brooklyn Bridge in the foreground, the Manhattan Bridge behind, and the great city of Brooklyn itself on the right.
With 2.5 million people, Brooklyn would be one of the largest cities in the US had it not merged with NYC in 1898.