THOMPSON YATES LABORATORIES REPORT 
bacteria present are comparatively few. More recently attention has been drawn to the 
nuisance which the green algae may create in certain waters, an example being recently 
described in the case of Belfast Lough by Professor Letts. Whether the blocking, 
which occurs in the coke or contact beds used in the various forms of bacterial treat- 
ment of sewage, may in part be due to the gelatinous material, which is associated 
with the very great production of zoogloea masses which occurs on and near the 
surface, I have not yet satisfied myself, but I have observed considerable blocking 
associated with the deposition of ferric oxide upon the coke, and it is probable that 
this ferric oxide is to a large extent dependent upon the action of the zoogloea masses. 
It will be gathered from the above remarks that the study of fungus deposits, 
whether occurring in sewage or water, is of considerable scientific interest, because in 
both cases a very active and special metabolism is taking place, which, in the one 
case, leads to the purification of sewage by the destruction of albuminoid matter and 
probably also by the assimilation of sulphur, and in the other to the removal of 
dissolved iron, but in both cases the disadvantages outweigh the advantages, and the 
study becomes one of very practical importance. Before describing the nature of the 
deposit in the Liverpool unfiltered water, I will briefly indicate the main features of 
the water supply. 
Description of the Lake Vyrnwy Water Supply 
The watershed is on the east side of the Berwyn range of hills in North Wales, the 
geological formation silurian (slate rock and Bala ash), the soil consists, to a large 
extent, of peaty moorland, and the water drains by innumerable streams into the 
artificial lake known as Lake Vyrnwy. The lake holds an immense volume of water, 
it is five miles long and three-quarters of a mile wide at its greatest width, and its 
maximum depth is eighty-four feet. 
The water passes from the lake through a fine straining copper gauge into the 
aqueduct, which consists, for the first two miles as well as for the final two miles, of 
tunnels driven through the rock and partly lined with brickwork, for the remainder 
of the twenty-five miles the water is conveyed through large iron pipes (forty-two 
inches internal diameter). 
Arrived at Oswestry the water collects in a storage reservoir, and from 
thence passes direct to the filter beds. 
From the filter beds the water is conveyed thirty miles by iron piping to 
Liverpool. 
Colour and Nature of the Water 
The striking feature of the unfiltered water is its yellow tint, which varies at 
different seasons ; the colour is removed to a considerable extent by the filtration. 
The water is very soft, it contains iron and manganese. 
