“In the 1960s, about 80 percent to 90 percent of the corals in the Keys were alive. Today, 94 percent of them are dead. […] The cause is septic drain fields in the low-lying Keys that leach nutrient-rich waste material into the groundwater and the ocean.”
http://www.palmbeachdailynews.com/news/content/news/2008/10/01/CoralReef1002.html