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In addition to grounds thus lost to shellfish, some 254,000 acres, 

 or 9 percent of the total area, are less desirable to finfish because of 

 organic, oil and thermal pollution. Oil pollution is a serious threat, 

 since the Chesapeake Bay is an extremely important wintering area for 

 waterfowl, including half of the 50,000 whistling swans in North America, 

 and more than 75 percent of the wintering population on the Atlantic 

 Flyway Canada Geese. A single oil spill in the upper Bay cost the lives 

 of 5,000 ducks. Many of the estuaries of the Chesapeake Bay are realized 

 or proposed sites of Nuclear Power Generating Plants which has prompted 

 a thermal pollution symposium. This has led to mortality of attached 

 plants and plankton, as will be elaborated upon in a later section. 



Aside from man-made stresses, the occurrence of two rooted aquatic 

 plants, introduced somehow from the Orient, have become a biological 

 nuisance in tidal waters. These are the Eurasian milfoil, Hyriophyllum 

 spicatum , and the water chestnut ( Eleocharis or Trapa? ) . The former 

 kills oysters by its smothering growth (up to 3 m) and also chokes out 

 valuable plants eaten by waterfowl. First detected in 1940, its explosive 

 growth led to the development of dense weed beds of approximately 100,000 

 acres by 1963. A disease subsequently reduced this coverage to 50,000 

 acres in 1966. The water chestnut which infested about 9,000 acres in 

 1939 has almost been eliminated from the Potomac River and its tributaries, 

 but other tributaries of the Chesapeake Bay still remained choked by this 

 weed. 



