Using GPS and state-of-the-art sonar, Columbia University researchers recently made the first comprehensive map of the wonders submerged in New York City's harbors. Supplementing those findings with historical data, New York magazine reported the inventory's highlights in May: a 350-foot steamship (downed in 1920), a freight train (derailed in 1865), 1,600 bars of silver (unrecovered since 1903), a fleet of Good Humor ice cream trucks (which form a reef for aquatic life), and so many junked cars near the Brooklyn and Manhattan Bridges that divers use them as underwater navigation points. Of most concern lately, though, are the wildlife: 4-foot-long...