THE FRESH-WATER LOCHS OF SCOTLAND. 
139 
source of water-siipiRy for the city of Edinburgh, objection was made to 
the water on account /)f the presence of certain organisms in it, and 
especially of the small crustacean (Daphnia) commonly called the Water- 
flea. It was pointed out at the time by those conversant with such 
matters that these Crustacea are usually present in all impounded waters, 
and we shall see that the organisms found in the water of St. Mary’s Loch 
are those which are characteristic of all freshwater lakes in this country, 
even of those which are reputed purest. Their presence does not, there- 
fore, in itself constitute any objection to the water. 
“ The water of St. Mary’s Loch was examined by the Lake Survey on 
two occasions, early in May, 1905, and in the middle of January, 1900. 
In May the water was fairly clear, and there were only a few species of 
animals and some microscopic plants found in it. There were four species 
of Crustacea : Diaptomus gracilis, Sars, Cyclops strenuus, Fischer, Daphnia 
hyalina, Leydig, and Bosmina ohtusirostris, Sars ; one rotifer, Notholca 
longispina, Kellicott ; and three diatoms, Asterionella formosa, Hass., 
Tahellaria fiocculosa, Kiitz., and T. fenestrata, Kiitz., var. asterionelloides, 
Grun. No other organism was at all abundant. 
“ All the species above enumerated are among the commonest of lacus- 
trine organisms, and it would be diflicult to find a loch in Scotland in 
which all of them are not present. 
“ In January the condition of the water was very different. The quantity 
of life was immensely greater, and rendered the water of a dull yellowish 
colour, and so turbid that bright objects could only be seen at a depth of 
about 3 feet. All the same sj^ecies were present, but some of them were 
more abundant than in May, and many species were present which were 
not found in May. The Crustacea were the same, but the larvae of the 
copepods were very abundant, and some of the Cyclops were carrying 
eggs. Of rotifers four additional species were found : Anurcea coclilearis, 
ConocMlns sp., Polyarthra platyptera, and Triarthra longiseta. The con- 
trast was greatest in the vegetable life. One greenish alga, forming little 
clusters easily visible to the naked eye, was mainly responsible for the 
turbidity of the water. 
“ This ‘flowering of the lake ’ in winter is not unfamiliar in Scotland, 
and has been seen in Loch Earn, etc. It takes place when the temperature 
is low (in St. Mary’s 38° Fabr.). As the increase of life is not due 
to high temperature, occurring, in fact, when the lochs are coolest, it may 
be supposed that pollution of the water by sewage may have something to 
do with it. At any rate, both St. Mary’s Loch and Loch Earn receive a 
good deal of sewage. These facts concern the open water of the loch, 
which alone is of much importance in relation to water-supply for towns. 
The life of the margin of St. Mary’s, and of the mud on the bottom, was 
also studied. 
“ The life of the margin, chiefly found among the mosses and other 
aquatic plants, is much more abundant than that of the open water. It 
