IV-567 



it may be so gradual as not to be noticed for many years. Many 

 studies of different aspects of estuarine biology have been made, 

 but there are only a few cases in which comprehensive ecological 

 studies have been made of pollutional effects. 



All of the 25 estuarine systems listed above also show some ecological 

 damage, but in 38 percent of the estuarine systems of the United 

 States there is not sufficient information to decide whether there 

 is no ecological damage, or whether there is just no easily 

 identifiable pollution problem present. 



The complex nature of pollution in the estuarine zone prevents the 

 separation of sources of pollution, kinds of pollution, and types 

 of environmental damage into neat compartments of cause and effect. 

 All of human activities in the estuarine zone can damage the 

 environment and most of them do. 



Wherever people live, work, and play in the estuarine zone the demands 

 of their social and economic activities place stresses on the bio- 

 physical environment. These stresses frequently result in degradation 

 of that environment, perhaps not immediately or even in a few years, 

 but nonetheless certain in its devastating final impact. 



