181 



In Dogfish Lake (Table VI.) the conditions are essentially 

 those of Quiver Lake, of which it is an arm. The principal 

 difference lies in the fact that flood water entering Quiver 

 Lake at low stages never moves as far up as our station in Dog- 

 fish Lake (PI. II.). Floods from Quiver Creek also merely back 

 up the clear water in Dogfish Lake without themselves invad- 

 ing that territory. The only flood silt entering this region is, 

 consequently, that which comes with general inundations. 



In Flag Lake (Table VII.) the conditions at inundation are 

 similar to those of other impounding backwaters. The great 

 amount of vegetation found here adds to both the vegetable 

 and the flocculent debris which roil the water whenever this is 

 disturbed by waves or the movements of fish. Turbidity, is 

 but rarely caused by plankton here, with the exception of the 

 few instances when diatoms or Oscillaria became very abun- 

 dant. The water is thus usually clear, the bottom being 

 commonly visible in the small spaces left free of vegetation, 

 even at a depth of 215 cm. 



In Phelps Lake (Table IX.) the silt conditions are peculiar. 

 The high level at which the lake lies and the intervening 

 stretch of bottom-lands (PI. II.) combine to keep out all silt- 

 laden flood-waters except those that enter by a now abandoned 

 channel from Spoon River or from the main stream at times 

 of their maximum floods. At other times the silt consists prin- 

 cipally of particles of bark and dust from the adjacent forests, or 

 of fragments of loam from the bottom, which is here unusually 

 stable. The comparative freedom from vegetation removes a 

 large element common in the silt of the other lakes. The turbid- 

 ity, however, is very marked in this lake, falling in many cases 

 below 20 cm., and in the majority of instances is largely due to 

 the very abundant plankton characteristic of its waters during 

 the greater part of the summer. Movements of fish and water- 

 fowl add considerably to the silt in suspension in this lake at 

 some seasons of the year. 



The color of the water has not been made a subject of 

 special inquiry. In general the turbidity gives it a grayish cast 



