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longer or shorter course, returns again to the river, whereas in 
the second it does not, consequently, all the fish that obtain 
access must be destroyed, unless proper precautions are taken, 
for it becomes a large fish trap. Precautions may be taken, 
and these are divisible into gratings fixed at the intake, or a 
periodic removal of fish from the reservoir back to the stream 
from which they had been abstracted. But the gratings are 
disliked by canal officers because they obstruct drifting objects 
and may choke the intake, so as a consequence they have no 
sympathy with their maintenance.* Another cause of the 
destruction of river fish is railway embankments; for when 
such extend some distance from the bank of a river, and the 
ground slopes away from the water, large lakes become formed, 
and as they subside all water connection with the contiguous 
river first becomes cut off, and subsequently, when they dry up, 
all the contained fish must necessarily perish. 
Pollutions may be so poisonous as to directly occasion the 
death of fish, and among such are mine washings, the refuse 
of manufactories, as those of gas or from paper mills, bleach- 
ing grounds, tanneries, sewers, &c. Likewise artificial root 
manures carried down from cultivated fields, sheep dippings, 
and many other deleterious substances, while the more rapid 
the current the more quickly do these poisons become diffused, 
and their injurious influences thus generally decreased. Some 
fish, as bull-heads, gudgeons, or loaches will thrive where 
salmon would die; and old fish sometimes survive where fry 
succumb. 
The modes of fishing may be injurious, and increased takes 
are not invariably symptomatic of improved fisheries, as such 
may be done at the expense of future years’ supply, while 
leaving only small parents to continue the race is a potent 
* H.M. Inspector of Fisheries has sanctioned that at some intakes at 
the Tamar, where a large quantity of samlets are reared for the Severn 
fisheries, that the legal grating be merely left in situ during such times as 
smolts are descending seawards, which period he fixed from February 14th 
until May 31st. At this period it was observed there were no leaves in the 
river. That many smolts migrate seawards, even in the autumn, appears to 
have been ignored or unknown: and this plan sanctioned in 188¢4 is still in force ! 
