491 



1909, to September, 1910, than in any year of our collection period 

 preceding the opening of the drainage canal. As the river contains, 

 generally speaking, a mixture of contributions from all its tributary 

 waters, the quantities of its plankton, particularly during the spring 

 months when these waters communicate with it most freely, are the 

 best obtainable index to plankton production in the whole system of 

 streams and lakes whose surplus water it carries away. Neverthe- 

 less, a comparative study of conditions in two highly typical bottom- 

 land lakes, so made as to show the effects in them of a change to 

 the new and higher water-level, wall have its special interest, partic- 

 ularly as it is in these bottom-land backwaters that most of the 

 fish fry are hatched, and spend, as a rule, the first weeks of their 

 existence. 



The Lake Plankton 



Thompson's Lake. — Thompson's Lake is a typical, permanent bot- 

 tom-land lake, continuously connected with the river at all stages of 

 water. In the higher stages the land between it and the main stream 

 is completely overflowed ; at medium stages the river water enters 

 at its upper end and flows out from its lower; but at the lowest 

 levels the lake is connected with the stream only by a narrow creek- 

 like outlet at its upper end. At six feet above "low water" it covers 

 nearly 3000 acres ; and at a river level of nine feet its area is about 

 4300 acres.* 



As will be seen from the following table, the plankton series of 

 Thompson's Lake for 1909-10 does not closely resemble any one of 

 the series of the earlier years, although the latter part of it, from 

 February to August, 19 10, is quite similar to the corresponding part 

 of the record for 1897-98. 



^Tabulation of Areas of Thompson Lake for the Various Water Elevations. 

 Report of the Submerged and Shore Lands Legislative Investigating Committee 

 (Forty-seventh General Assembly), Vol. L p. i7i. 



