The Chinese have been draining coastal wetlands for the rich soils they yield for 6,000 years. Other causes of extensive coastal habitat destruction include the rapidly expanding fish farming industry, timber extraction, and civil engineering projects that alter the flow of sediments and fresh water. The wetlands at the mouth of the Mississippi River are eroding away at a rate of 150 square kilometers per year, largely due to flood control and channeling projects in the delta and upstream. Worldwide, about half of all salt marshes and mangrove swamps have been cleared, drained, diked, or filled, and few estuaries remain unpolluted or unaltered. Offshore, coral reefs, kelp forests, sea grass beds, and other shallow water habitats are endangered by the combination of direct destruction and pollution from land.
Coral reefs are of particular concern.
They line more than 100,000 kilometers of coast and harbor a large portion of the coasts' biological wealth. Unfortunately, they are highly vulnerable to changes in their environment. If the normally clear tropical waters they form in are clouded by pollutants, for example, the corals can't photosynthesize to produce their food. They also recover slowly when damaged. Other offshore habitats, likewise, suffer from such habitat degradation.