24 U. S. BUREAU OF FISHERIES. 
It is well to paint the pipes with waterproof paint, and a mixture of graphite 
and oil is recommended for use in the elbow and coupling threads. Pipe 
threads should penetrate elbow 1 inch, hand screwed. When the drainage line 
is to be of terra cotta its joints should be sealed with cement throughout the 
line rather than laid partly open, as is sometimes done. 
The elbow and two pieces of threaded pipe comprising the outlet proper and 
modifications as to size and detail of the L outlet and appurtenances may 
be made to suit requirements and material available. If it is necessary to 
reduce expense, the kettles may be reduced or omitted entirel¥, but the installa- 
tion of a kettle, even though of small size, is recommended because of its use- 
fulness when drawing the pond and sorting the fish. The cement blocks, the 
chief use of which is to protect the outlet drainage line against water working 
an opening about it, and which also prevents animals such as crayfish and 
muskrats following it through the embankment, must not be omitted because 
without the blocks to protect and stay the drainage line leakage is certain to 
occur. The depth of these blocks should not be reduced, but in unfavorable 
soil may be increased to advantage. 
All surfaces over which embankments are to be laid should be plowed before 
the fill is commenced, so that the earth will bind satisfactorily, and all foreign 
matter such as brush, rock, etc., should be excluded from the fill dirt. 
The outlet is placed at the drain point and stayed as described, after which 
the fill is laid over it, the outlet being ready for service as soon as the fill is 
started. Pipe 4 to 6 inches in diameter is sufficiently large for ponds of less 
than 1 acre in area. It is always better to have the outlet pipe too large 
rather than too small. 
Many of the spiilways and outlets in general use give more or less trouble 
through leakage, and those of cement construction often freeze and crack, or 
settle and crack, causing serious trouble and considerable expense. Many of 
the outlets in use are built into the embankment, thereby weakening and sub- 
jecting the embankment to the danger of washouts. Loss of fishes often arises 
from screens below the water surface becoming damaged, and many outlets, 
when the pond is being drawn, have too much suction for the good of the little 
fish. These and other troubles have been eliminated in the L outlet, some 
favorable features of which are enumerated below: 
The action of the outlet is quick and easy. 
Leakage and freezing difficulties have been overcome. 
The outlet operating from the surface provides minimum suction, which 
works to the benefit of small fish. 
The screen is visible, therefore safe, and easily cleaned. 
The outlet does not weaken the pond embankment. 
The outlet may be assembled, installed, and maintained at low cost, and 
is so simple of construction that any “handy man” can build and install it. 
ERADICATION OF SOME OBJECTIONABLE PLANTS. 
The rank growth of cat-tails in ponds and lakes, particularly at 
fish-cultural stations, has often become a serious nuisance, causing a 
substantial reduction in the effective area of the pond. Hitherto 
there has been no inexpensive or practicable method of combating 
them, since removal by cutting alone is quite ineffectual. Superin- 
tendent Canfield has devised and demonstrated the efficacy of a 
method of elimination of these plants, based upon the necessity of 
areation through contact of the plant or its landward roots with 
the air. 
The water level in the pond is lowered below the limit of growth 
of the cat-tails, which should then be mowed as low as practicable. 
With spade or plow a ditch is made below the normal water line and 
between the cat-tails and the shore. The ditch must be sufficiently 
deep to sever the roots that connect the plants in the pond with the 
shore or with any plants that are allowed to remain above the ditch. 
In this way the air supply from the land roots is completely cut 
off. The pond should then be immediately flooded and the water 
