10 FISH PONDS ON FARMS, 
jacently located, provided the intake is adequately screened, the 
supply arranged so that it can be cut off during times of excessive 
turbidity, and measures are taken to prevent the inundation of the 
pond site in high-water periods. 
It may be necessary to erect a dam in the channel of the stream, to 
provide the required head of water for a gravity flow to the pond, in 
which case it may be of a simple type, designed merely to accomplish 
the end in view. The intake from the stream should be wide and 
deep, thus presenting a large screen surface to obviate the complete 
stoppage of the water supply in the absence of the caretaker. It 
should be covered by a series of screens graduated in size, the first 
to consist of coarse hog wire, or wooden racks with like openings, to 
catch the largest objects. The intermediate screen (of 2-inch mesh) 
will intercept vegetation, while the inner one must be fine enough to 
exclude smaller débris and the fry of undesirable fishes. Immedi- 
ately below the screens, gates should be provided so that the water 
may be shut off at will and diverted into a storm channel when it 
becomes too roily for use. 
Where the source of supply is a lake the difficulties referred to 
above are not encountered, lake -water seldom being roily and de- 
manding less attention to screens owing to absence of currents. 
Uncontaminated open waters have many advantages. Their tem- 
peratures are seasonal; usually there are no abnormal gaseous con- 
stituents to be corrected; the plankton or pelagic animal and plant 
life contained therein forms a valuable addition to the natural food 
supply in the pond, and were it not for the difficulty of control and 
occasional roilyness, such waters would be preferable to springs and 
wells as a source of supply to fish ponds. 
Wells, both flowing and power lifted, are successfully used in some 
sections for the cultivation of fish. Before incurring the expense of 
constructing ponds to be supplied from such a source, however, it 
will be advisable to thoroughly test the water in order to demonstrate 
its fitness for fish culture. This can best be done by fitting up a 
running-water supply in a retaining reservoir, and holding therein, 
for an extended period, a number of specimens of the species of fish 
it is desired to propagate. If they thrive, it may be assumed that 
the water is free from injurious gases or mineral substances and is 
adapted to the work it is proposed to undertake. 
Rain WATER (SURFACE DRAINAGE).—Another class of ponds avail- 
able for the propagation of fish, known as “sky ponds,” embraces 
those wholly or partly dependent upon local precipitation for their 
supply of water. Such ponds are invariably profuse in the produc- 
tion of fish food, and for this reason would be ideal were there an 
auxiliary water supply adequate to maintain constant surface levels 
during the critical nesting season, and a fair depth throughout the 
