It is estimated that 220 million acres of wetlands existed in the coterminous U.S. (lower 48 states) in colonial times. Today, less than half remain (about 100 million acres). Roughly 5% of the lower 48 states contains wetlands. Alaska alone possesses over 200 million acres, more than twice the acreage of all other states combined.
States with more than 20% of their land area represented by wetlands are Alaska (48%), Louisiana (36%), Florida (33%), Maine (26%), Minnesota (21%), and South Carolina (21%). Those with 10-20% of their land mass in wetlands are New Jersey (19%), Delaware (18%), Georgia (18%), North Carolina (16%), Wisconsin (15%), Michigan (15%), Mississippi (14%), Massachusetts (12%), and Arkansas (10%). States with less than 1% of their territory occupied by wetlands are Montana (0.9%), Arizona (0.8%), Kansas (0.8%), Idaho (0.7%), Nevada (0.6%), New Mexico (0.6%), California (0.5%), and West Virginia (0.4%).
From the mid-1950s to the mid-1970s, the coterminous U.S. lost an average of 458,000 acres of wetland per year. Between the mid-1970s to the mid-1980s, the loss rate drop to about 290,000 acres/year. Today, the annual loss rate is somewhere between 70,000-110,000 acres. The dramatic decline in wetland losses is attributed to wetland regulations (federal and state), to improvements in land use policies (discourage wetland filling), and more recently, to government-sponsored wetland restoration projects (to increase wetland acreage by either bringing hydrology back to formerly drained wetlands or by improving the functions of previously altered wetlands).
Although wetlands are receiving better protection today than in the past, wetland losses still continue. The largest losses in the U.S. are probably taking place in the Southeast (states including Florida, Georgia, South Carolina, North Carolina, Louisiana, Arkansas, and Mississippi). Most of these states are losing forested wetlands to agriculture, yet recent agricultural policies may be reducing this type of wetland conversion. Louisiana is losing coastal wetlands to submergence - estimated at 50 square miles per year. The factors causing subsidence of Louisiana's coastal plain are complicated (sea level rise and salt water intrusion up estuaries, oil drilling, construction of navigation canals, diking of coastal marshes, levee construction, groundwater extraction, and diversion of the Mississippi River).
The U.S. Fish and Wildlife Service will be publishing a national report on wetland trends in December 2000. This report will detail the extent and nature of wetland losses from the 1980s into the 1990s.