FIELD BOOK OF PONDS AND STREAMS 



distribution of algae in clear, deep lakes have shown that they 

 cannot get light enough except in the upper fifty or sixty 

 feet of water, and even in the lower levels of that they are 

 very rare. The main population of green plants and animals 

 lives only where light is abundant. Consequently shallow 

 ponds are inhabited down to the bottom, but in large, deep 

 lakes life extends through only a small proportion of the 

 depths. 



10 



