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: 



