11 



Althougli our information from, and observations on the 

 river have verified the fact as to the diminution in the upper 

 waters, and an increase about and below the Great Fails, we 

 are, however, not prepared to accept the generally accredited 

 theory which accounts for the decrease on the supposition 

 that they are driven to feed on each other by the exhaustion 

 of their food supply. Although we do not deny that the Bass 

 will devour the young of its species, as will the Trout and 

 other fishes — even the Gold fish, when driven to do so by a 

 want of food — we are inclined to believe that the conditions 

 existing on the Potomac are attributable to other caases« 

 First, and the most potent of these is, the existence of the 

 impassable barriers to the upward ascent of the fishes which 

 are at all migratory in their habits, the six or seven dams 

 thrown across the river to back up the water, in order to 

 supply the Chesapeake and Ohio Canal, and the impassable 

 "Great Falls," situated about fourteen miles from "Wash- 

 ington. 



On the approach of cold weather in the Fall, the fish natur- 

 ally work down stream, seeking the deep holes in which to 

 pass their Winter mouths of semi-hybernation. Many of 

 them, natives of the upper levels, passing over the canal dams 

 and the Falls in their downward migration, on the approach 

 of Spring are prevented from again reaching the localities 

 left on the approach of cold weather. They spawn, and 

 their young are raised in the lower levels. In this way they 

 have gradually worked down the river, the decrease in the 

 upper waters being followed by a consequent increase in the 

 lower levels. 



This interruption, to which we have referred, has no doubt 

 been the most potent instrument in the unequal distribution 

 of the fish in the river. 



Another cause to which the decrease even on the same 

 levels should be attributed, is the existence in large numbers 

 of "fish-traps" or "fish-weirs." 



The Potomac river, from Piedmont to the Great Falls, 

 though there exists between these points no insurmountable 



