CHAPTER VII 



SALT MARSH DRAINAGE 



THE SALT MARSH PROBLEM IN GENERAL 



The salt marshes that abound along the Eastern and Southern 

 coasts of the United States from New York to Mexico constitute 

 probably the greatest single breeder of mosquitoes in the country. 



These low-lying marshes, swept from time to time by the tides, 

 which fill every hole and depression, make ideal breeding places 

 and present probably the most difficult problem that there is 

 from an anti-mosquito point of view, not only on account of the 

 huge areas they cover, but also on account of the enormous 

 expense involved. 



Fortunately, not all parts of the salt marsh breed mosquitoes 

 in equal abundance, owing to the activities of larva-destroying 

 fish, which, when they are present in considerable numbers, eat 

 the larvae nearly as fast as they hatch from the eggs. However, 

 there are many parts of the marsh that the fish cannot reach, such 

 as high-lying and shut-in meadows over which the tides rise only 

 occasionally. Even where an extra high tide has stocked the 

 holes with fish, the water soon dries up and the fish die; then, rain 

 water fills the holes, larva appear and a brood of mosquitoes 

 gets on the wing. 



The problem of preventing mosquito breeding in salt marshes 

 is thus seen to be one of determining just what parts of the marsh 

 constitute mosquito production areas and then so treating them 

 that the tide-water will run off at frequent intervals, will be 

 constantly stocked with larva-destroying fish or will be kept out 

 altogether. The methods of accomplishing these results are 

 ditching, filling and diking and tide-gating. 



AGRICULTURAL VS. ANTI-MOSQUITO MARSH DRAINAGE 



In the drainage of salt marshes, as in upland drainage, there is a 

 distinction between drainage for agricultural purposes and drain- 

 age for anti-mosquito purposes. As a general rule, it may be said 



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