By the ordinary process of multiplication, if unchecked by other untoward influences, the supply of fish in such a river must ahva}'s be in excess of the number caught with hook and line. But there are other pernicious influences, among them the pollution which results from sewage in the vicinity of large towns. There can be little doubt that fish are poisoned by the fouling of the element in which they live. It may be too that the constant accretion of cinders and ashes upon the bed of the channels has ]3revented the development of those forms of life upon which the fish depend for food. That this view is not entirely fanciful the reader will readily see if he will take paper and pencil, and with such data as he may have at hand calculate the number of steamers that have dumped their ashpans in the river in the ]3ast threescore years. A million tons would fall far short of the probable deposit. The restocking of the waters will only be an efficient remedy in places where the fry will not be subject to the disadvantages we have suggested and others of equal importance. It is well known that man}% if not all, of the fish that frequent the Hudson, or any large river, run into the smaller streams to spawn. The practical closing of many such streams by means of dams, where no fish-ways are provided, must of necessity militate greath' against the natural increase.

442 The Hudson River