Outside Miami's Biscayne Bay, coral reefs that were once a vivid rainbow have been turned a barren gray, choked in sediment, by a dredging operation run by the U.S. Army Corps of Engineers.

The Port of Miami is dredging its shipping channel in the hope of luring the mammoth cargo ships that will sail through the widened Panama Canal when that work is finished in 2016. Port Everglades in neighboring Fort Lauderdale, which is even richer in coral than Miami, plans to dredge its channel in two years.

Up and down the East Coast, ports are competing to attract the "post-Panamax" freighters, but South Florida is different: The dredging here inflicts damage—some say irreparable damage—on North America's only coral