Since the 1700s, more than half of all of the wetlands in the lower 48 states have been lost, and although there are no reliable statistics that deal solely with coastal wetlands, several factors point to the loss of coastal wetlands as being at least as severe as the loss of wetlands overall. A U.S. Fish and Wildlife Service report estimates that by the mid 1970s, over half of all saltmarshes and mangrove forests present in pre-colonial times had been destroyed. Florida and Louisiana, two coastal states with the greatest acreage of wetlands, have lost about half of their original wetland area. Louisiana alone is losing between 16,000 and 25,000 acres of wetlands a year, which is the highest sustained wetland loss rate in the country. Most of that loss is occurring in coastal areas.
Many factors are responsible for coastal wetland loss.
In the early part of this century, coastal wetlands were drained and used for farming or grazing. More recently, coastal wetlands have been filled or dredged for roads, houses, golf courses, marinas, and other development. In Louisiana, where most of the country's coastal wetland loss is occurring, wetlands are being lost to open water due to a combination of factors including canals dredged through the marshes, dams on the Mississippi River reducing sediment to the marshes, land subsidence, and sea level rise. Even wetlands that are not actually filled or dredged are becoming degraded due to pollution, changes in water flows, and invasion by weeds or other non-native plants and animals. Coastal wetland losses can be directly traced to population pressures and other human changes occurring along the coast.