Reclamation of wetlands
The federal government, through a series of legislative acts between the 1850s and 1970s, encouraged the draining of swampland and the reclamation of wetlands for farming and for the elimination of mosquito breeding grounds. In California, this led to intensive efforts in the 1860s to build levees and drains, particularly along the Sacramento River and in the Delta. By the 1920s, an estimated 70 percent of wetland acreage had already been modified by drainage and reclamation efforts.
The situation changed in the 1970s, when policy setters became convinced of the important environmental functions of wetlands. These include reducing flood peaks by detaining storm flows, protecting coastal areas from wave erosion, and recharge groundwater supplies. The protection and restoration of some wetlands is now legislatively encouraged.