Last week, 200 leaders in the environmental movement gathered in New Orleans for the eighth ecological symposium organized by the Orthodox Christian Church. Participants included leading scientists and theologians, politicians and policy makers, business leaders and NGOs, environmentalists and journalists. Similar conferences have taken place on the Adriatic, Aegean, Baltic, and Black Seas, the Danube and Amazon Rivers, and the Arctic Ocean. This time we sailed the mighty Mississippi to consider its profound impact on the U.S. and its fate within the global environment.

It...