PROTECTION OF RIVER AND HARBOR WATERS 7 



total Hood is 11,030, so that the net outflow is proportionately small. In 

 the Hudson River the ebb is 0,910 million cubic feet and the flood 5,740 

 million. In the East River the figures are respectively 4,068 million and 

 3,908 million cubic feet and in the Harlem River 176 million and 153 mil- 

 lion. The result is that most of the sewage oscillates back and forth instead 

 of passing promptly out to sea. 



The general effect of this pollution is manifest in the reduced oxygen 

 content of the harbor. The East River above Hell Gate contains on the 



Gathering driftwood from the polluted waters about the steps of the Battery. Photo- 

 graph from a model in the American Museum 



flood tide 92 percent and on the ebb tide 80 per cent of the oxygen necessary 

 for saturation. Below Hell Gate the values fall to 69 per cent on the flood 

 and 60 per cent on the ebb. In the Hudson River above Spuyten Duyvil 

 there is about 84 per cent of the oxygen necessary for saturation, on both 

 tides; below Spuyten Duyvil the figure falls to 76 per cent on the flood and 

 66 per cent on the ebb. Samples taken from the eastern end of the Harlem 

 show on the average only 43 per cent of the oxygen necessary for saturation 

 on the flood tide and only 27 per cent on the ebb. The upper East River 



