20 Artificial Aquatic Habitats 



weather. In dry years such a pond could become useless both for water 

 supply and recreation. 



Farm ponds usually range in size from /i acre to several acres. Those 

 smaller than about 1 acre are unsatisfactory for fishing. Often when a 

 pond or lake is planned to exceed 10 acres, the builder has in mind some 

 commercial use, rather than farm water supply and recreation. 



WHEN IS A POND A LAKE? 



a 



The question of when a body of water is a lake and when it is a pond 

 has never been settled to everyone's satisfaction. According to some 

 limnologists,^^ "A lake is thermally stratified, through most of the year, into 

 an epi-, meta-, and hypolimnion.* Only a body of water conforming to 

 this specification will be considered when using the term lake." [asterisk 

 mine] To many this definition is unsatisfactory because most small ponds 

 built by damming steep-sided ravines are thermally stratified "through 

 most of the year," although the stratification is such that the upper edge 

 of the hypolimnion may be indefinite. In contrast, it seems illogical to 

 call a large, shallow body of water a pond; for example, Chautauqua 

 Lake, a natural basin in the floodplain of the Illinois River valley near 

 Havana, Illinois, almost never shows thermal stratification. By definition 

 this lake should be considered a pond, although it has a surface area of 

 nearly 3500 acres. 



In Oklahoma, 10 acres represents the point of separation between lakes 

 and ponds; thus bodies of water with less than this surface area are ponds 

 and those above it, lakes. ^^ However, Dr. W. C. Starrett suggests that the 

 point of separation be set at 4 acres, and Humphrys and Veatch ^^ con- 

 sider Michigan waters of less than 5 acres as "lakelets and ponds." In 

 any case, if we are not to use the terms interchangeably, the separation 

 should be based on an arbitrary upper size-limit for ponds, and any 

 body of standing water above this limit should automatically be con- 

 sidered a lake, regardless of its limnological characteristics. 



ARTIFICIAL LAKES FOR DOMESTIC USES 



A great many artificial lakes have been constructed throughout tlie 

 United States for urban and/or industrial water supplies. These artificial 

 impoundments may vary in size from a few hundred acres to many 

 thousands of acres. On these lakes, recreation is of secondary importance 

 to water-supply uses, although an effort often is made to sell the reservoir 

 to the public on the basis of its recreational attractions. 



* Epilimnion ( upper lake ) , metalimnion ( middle lake or thermocline ) , liypolimnion 

 (lower lake). 



