THE SALMON AND WATER TEMPERATURE 143 
should be considered a tributary or a separate river 
entering a common estuary. This is the case with 
the Earn, which enters the tidal waters of the Tay, 
and but for obstructions in the Earn I believe that 
spring fish would ascend more freely than they do. 
In the case, however, of the Lochy on the west 
coast we have another instance worth referring to. 
The river Lochy formerly flowed naturally from Loch 
Lochy into the sea near Banavie; when, however, 
the Caledonian Canal was constructed the course of 
the Lochy was to some extent utilised, and the river 
was given a new and artificially cut channel from 
the loch into the Spean at Muccomer. The Spean, 
coming as it does from the very high land to the 
north and east of Ben Nevis, is a cold river, while 
the Lochy water, like the Ness at the northern 
end of the great chain of lakes which form the 
Caledonian Canal, is warm. Early fish ascend the 
Lochy to Muccomer, and there pause. They are, 
unfortunately, obstructed by a fall with a very 
inadequate fish pass from farther ascending the 
Lochy, so they remain in the large Muccomer pool 
till the Spean water has lost its forbidding tempera- 
ture, when they ascend that river. Such fish as do 
manage to ascend the Lochy do not do so before 
the ascent of the Spean is well begun. The reason 
for this has already been explained. We see, there- 
fore, that while early as compared with late rivers 
appear to present no definite distinction of tempera- 
ture, the habits of ascent in all rivers are very 
considerably influenced by thermal conditions. All 
our Scottish rivers are colder than the surrounding 
