IV-144 



300 square miles of wetlands that originally surrounded San Francisco 

 Bay have been filled. San Francisco Bay is not unique. Table IV. 2. 

 10 lists areas of basic marsh and wetland habitat filled 1n the past 

 20 years. (Figure IV. 2. 26.) Expanding residential and commercial 

 needs for more shoreline land and navigation spoil disposal require- 

 ments are the major causes of dredging and filling operations. 



Two-thirds of the total marsh and wetland areas are important fish 

 and wildlife habitat. Since the late 1940's, seven percent of the 

 important habitat has been lost; the largest single block of this 

 has been in the San Francisco Bay system, where much of the tidal 

 marsh and shallow waters no longer exist. 



The patterns of filling estuarine marsh and shallow water areas 

 closely parallel population and industrial development within the 

 estuarine zone. In North Atlantic and Middle Atlantic regions 

 commercial development has been the major cause of the filling of 

 estaarine areas; in Florida (which has parts in three biophysical 

 regions) residential development has been the major reason for 

 filling; in both Louisiana and Texas dredging and filling associated 

 with oil and gas exploration has been the aajor cause for estuarine 

 physical modification. 



Estuarine modifications due to control and regulation of tributary 

 freshwater streams may be unsought consequences rather than delib- 

 erate developmental schemes. Many of the Nation's major river 



