of the Fishery Board for Scotland. 



17 



The Loch More dam dyke raises the level of the loch twelve feet. 

 The purpose is to impound such a quantity of water as will enable 

 artificial floods to be let down at will. This action has been taken 

 in view of the success of the Badanloch dyke on the Helmsdale. 

 In future, therefore, when the Thurso runs too low, when fish 

 become stale from lying long in one pool, or when fish in the 

 estuary are unable to ascend for lack of water, a flood or distinct 

 rise of water will be let down. 



The dam and fish pass were designed by Mr. P. D. Malloch. 

 The dyke is in the form of an obtuse angle, the apex being at the 

 natural river outlet. The arm of the an^le which runs to the 

 right bank has a bye-wash overflow for storm water ; the arm to 

 the left bank is the longer of the two, and has running alongside 

 of it the gradually ascending salmon pass. The angled design of 

 the dam dyke is apparently in order to allow an easy gradient in 

 the pass. The wall at the angle of the dyke is 17 feet high, and 

 the length of the main overflow is 310 feet. The fish pass is 200 

 feet long, 12 feet wide at the top and 25 feet wide at the bottom ; 

 it has a gradient of 1 in 20. To act as breaks to the descending 

 w r ater, row T s of stones are erected at intervals in the manner which 

 has become familiar in passes recently designed by Mr. Malloch. 

 This arrangement is sufficiently well seen in the photographs of 

 the Loch Vennacher Pass already given. To allow of fish entering 

 the loch at different levels, two openings or passages through the 

 dam dyke, at right angles to the direction of the pass, are provided. 

 These openings are each three feet square and sluiced. 



It is possible, I noticed, for one or other of those sluices to give 

 only two feet of water. This thins out very much on the right or 

 sluiced side of the pass ; yet even with this amount the broken 

 water in the lower pass is very noticeable. The ascent by spring 

 fish should be carefully watched for. 



Loch More used to be about 170 acres in extent, to have an 

 average depth of 6' 10" and a maximum depth of 15 feet. Now 

 the surface area is increased to 511 acres and the maximum depth 

 to 27 feet. Salmon rose to the fly in any part of the loch, and 

 the habit was for the angler to cast over any part of the loch. In 

 future, I am informed by Mr. Keith, the factor, and chairman of 

 the District Fishery Board, that the loch is to be divided into 

 eight beats, corresponding to the eight beats of the river below the 

 loch. 



Purification of Rivers by Bacterial Methods. 



During the year my attention has been specially directed to the 

 treatment of sewage and other polluting matters by what are known 

 as " bacterial methods." 



These methods have been developed to a considerable extent 

 during recent years, and a Royal Commission, under the chairman- 

 ship of the Earl of Iddesleigh, is now investigating their merits. 



There are many varieties of these methods of treatment, but in 

 all of them the purification of the organic matter is effected by 

 means of bacteria, in artificially-constructed filters. Scientifically, 



