56 Interrelationships of Fishes and Lake Habitats 



flos-aquae, is known to release a very toxic substance when it dies and 

 decays; and a secondary cause of death may have been direct poisoning. 

 Jackson and Starrett ^^ described locahzed kills of fishes ( mostly gizzard 

 shad ) in Lake Chautauqua on July 9, 1953, that apparently resulted from 

 localized oxygen deficiencies. At 6:20 a.m. the dissolved oxygen content 

 at one point was only 1.6 ppm, and later several fish were observed that 

 presumably had died of asphyxiation. The weather was hot and the lake 

 very quiet. 



OTHER DANGERS OF IMPOUNDMENTS 



Fishes in small artificial ponds and lakes may be decimated by some 

 "accidents'" that occur because of the physical aspects of these impound- 

 ments and the fact that men are careless by nature. These "accidents" 

 are mentioned here so that they may be recognized and avoided. 



Loss OF Ponds Because of Burrowing Animals 



Small ponds are sometimes subjected to washouts through the activities 

 of burrowing crayfish, muskrats, rats, and other burrowing mammals. 

 These animals usually work in the dam, digging tunnels above the normal 

 water level of the pond. No damage appears until a heavy sudden rain 

 raises the pond level well above normal, and the tunnels become water 

 channels through which water escapes to the downstream side of the 

 dam usually taking with it a section of the earth fill and all of the water 

 and fish in the pond. 



It is usually impractical to bury wire mesh or metal sheeting in small 

 dams to prevent damage from burrowing animals. The best solution is 

 to maintain a constant vigilance and trap or poison the rodents when they 

 appear to be damaging the pond dam. Burrowing crayfish are sometimes 

 killed by dropping one or more crystals of crude copper sulfate in their 

 holes or "chimneys," or by adding either one teaspoonful of carbide 

 powder or two ounces of stock dip solution to each burrow and then 

 tamping the burrow shut.^ On ponds larger than 3 or 4 acres, the dams 

 are so wide at the top that there is little danger from burrowing animals. 



Wind Action 



When artificial lakes and dams are too large to be subject to damage 

 from burrowing animals, prevailing winds acting on such a wide surface 

 can create another danger by blowing parallel to the long axes of the 

 lakes, thus causing waves and currents that cut earth from the fills at 

 the water line. Unless a fill is protected by rip-rapping of concrete, rocks, 

 or by a floating boom, the action of the waves may gradually cut away 

 the dam. Wind and wave action can occur in any part of the lake, often 



