ELEVENTH ANNUAL REPORT. 99 



be free from sods or other matter liable to decay. The ground 

 cleared for the embankment should have a ditch extending its 

 full length into which the new earth will settle, thus increasing the 

 stability of the dam. 



The embankment of the dam if it is to be six feet high should 

 be ten or twelve feet wide at the base and four feet broad on top. 

 The earth used in its construction will naturally be derived from 

 the bottom of the proposed pond, which will, of course, serve 

 to increase its depth. 



The overflow should be large enough to carry off the surplus, 

 when the water is high, without danger to the dam and the outlets 

 in general should be screened with wire netting to prevent the 

 escape of fishes. The drain for drawing off the water should, of 

 course, be put in place before the dam is thrown up. Earthen 

 drain-pipes are risky, as no matter how closely the joints may be 

 set and cemented, plant roots will eventually find their way in- 

 side and clog them up. Iron pipe of not less than four inches 

 diameter, with the joints well soldered, is more reliable. A 

 hollow log will serve the purpose of a drain-pipe, and wear well. 



If the drain, or bottom outlet, is built of concrete and large 

 enough to be conveniently cleared, it would be more effective in 

 lowering a large area of water. The upper end of the drain 

 should fit tightly into the foot of the upright penstock in the pond. 



The penstock itself is merely an upright drain or sluice of 

 planks or concrete, having about the same capacity as the drain- 

 pipe itself. It is fitted on one side with short "water boards" 

 sliding in grooves which can be removed one after another, to 

 permit the escape of the water. A heavy plank should connect 

 the head of the penstock with the top of the dam. 



Before the new pond is filled, all roots, stumps, rocks and every- 

 thing else that would prevent the free sweep of a net along the 

 bottom, should be removed. 



All ponds, whether natviral or artificial, accumulate debris of 

 which they can not be cleared, except when empty. A muddy 

 pond will give the fish a muddy flavor. When the pond is being 

 cleaned, it is necessary to remove the fishes from the deep hole or 

 kettle. Any attempt to remove decayed matter and sediment, 

 while fishes still occupy the deeper portions of a pond, may be 

 fatal to them, as dangerous gases are then liberated among the 

 crowded fishes. If the pond is very foul, it should be only par- 

 tially lowered at first and the fishes removed with a seine. 



With a reserve pond or two, it is possible, not only to thor- 

 oughly clean a pond, but to "winter" it : that is, leave the bottom 



