REPORT OF THE SUPERINTENDENT OF THE BIOLOGICAL STATION. 



To the Director of the Ldhoratorij. 



Sir : The past two years have offered new and interesting 

 conditions in the environment in which the work of the Illinois 

 Biological Station has been prosecuted. The period of 1894 

 and 1895 was one of typical low water, without an extensive, 

 rise of the river during the spring and early summer, when such 

 floods usually occur. On the other hand, these years were not 

 marked by long uninterrupted periods of very low water. Under 

 these conditions of two years of generally low water, without 

 marked fluctuations, the lakes w-ere thorouglily choked with 

 vegetation, and even the banks of the river itself became fringed 

 with a rank aquatic growth. A rise to 12.6 feet, culminating 

 January 6, 1896, was succeeded by a series of minor floods at 

 intervals of about two months throughout the year. The net 

 result was an increase in the average height of the river for the 

 year, which was 6.87 feet above low- water mark — fully two 

 feet above that of the average for the two years preceding. 

 This was, then, a high-water year, without marked fluctua- 

 tions, and the result was that the vegetation remained to 

 a considerable extent in the lakes and the river. The year 

 1897 opened with rising water, which culminated January 28 at 

 12.9 feet, while a subsequent rise on March 27 reached a height 

 of sixteen feet — the highest point attained since 1892. (See 

 Plate II.) From this maximum the river fell slowly through 

 the four months that followed, reaching a minimum early in 

 August. From this time until the close of the year, in conse- 

 quence of a general drought throughout the State, low water 

 persisted, there being only a slight rise as evaporation was 

 checked during the cooler weather of autumn. In spite of 

 the long-continued low water the average height for the year 

 was 6.9 feet — a slight increase over the preceding year. There 

 was thus present the somewhat unusual condition of long- 

 continued high water during the first half of the year followed 

 by an uninterrupted period of unusually low water in the 

 second half, the change from the one to the other being quite 

 abrupt. Under these circumstances the vegetation was largely 

 removed or its excessive growth "prevented. The contrast 



