820 KEPORT OF COMMISSIONER OF FISH AND FISHERIES. [6] 



regions called the "Hautes-Fagnes," which at tlieir highest point rise 

 to a height of 700 meters. The Lake of Gileppe, which has thus been 

 formed, has an area of 800,000 square meters, and the water in tlie dam 

 has a depth, varying from 25 to 45 meters. 



Here I would advise the introduction of the great lake trout {Salmo 

 lacustris) and the trout of the Alps {Salmo salvelinus), of the Coregona 

 /era, and of certain American salmonoids which do not go into the sea, 

 and which would find all possible levels for spawning from the dam to 

 the river flowing in its pebbly bed and feeding the lake. 



Our minister of public works commissioned M. de Clercq, chief engi- 

 neer of bridges and roads, to prepare some propositions as to the best 

 mode of repopulating the navigable rivers. The remarkable work of 

 this skilled engineer was published in 1881. 



The propositions which he makes for remedying the depopulation of 

 our waters are classed in the following order : 



(1.) To prevent the pollution of the waters. 



(2.) To prohibit the destruction of sedentary fish during the spawn- 

 ing season, and to regulate the catching of migratory fish. 



(3.) To construct fishways at all dams in the Meuse and its tribu- 

 taries which are too high for the salmon to leap over. 



(4.) To arrange spawning-places where the fish find all the conditions 

 favorable to reproduction. 



(5.) To engage in practical fish-culture as far as the salmonoids are 

 concerned. 



These various points are carefully treated by a man fully competent 

 to do justice to the subject. I will quote what he says relative to the 

 jiollution of the waters, because this is, in my opinion, the principal 

 obstacle in the way of repopulation : 



" There can be no question of prohibiting industries which are closely 

 interwoven with the general welfare of our country, but it is important 

 to i^rohibit the throwing of substances into the water without having 

 been treated in the most efficient manner for freeing it from those sub- 

 stances which are hurtful to fish, and at least as much so to other 

 animals which drink this polluted water. The pollution cannot be con- 

 sidered as sufficiently weakened unless the waters are rendered fit for 

 fish to live in." 



There is another chapter in this work which will repay careful perusal, 

 the one in which M. de Clercq describes in detail the construction of 

 good salmon-ways, and indicates the defects which make some salmon- 

 ways worthless. We must here point out, in a humbler sphere than the 

 management of great rivers and the interests of the salmon fisheries, 

 the obstacle which many water-mills present to the repopulating the 

 small streams. I refer to those mills which are placed near small water- 

 courses in plains which have but a slight grade. When the mill is not 

 placed on a channel branching ofl" from the river, but blocks the river 

 entirely, it interrupts the circulation of the fish. The level of the water 

 will under these circumstances vary constantly : sometim es, when the 



