447 



The comparison of backwater and channel production in 

 1898 is in some contrast with that in 1897. In 1897, omitting 

 Spoon River, production in backwaters exceeded that in the 

 channel in 29 of 40 monthly averages, or in 73 per cent., while 

 in 1898 the excess occurs only in 26 of 37, or in 67 per cent. 

 The excess, moreover, is frequently of less amplitude in the lat- 

 ter year, as is seen in the relation of the means of the monthly 

 averages of backwaters and channel in the two years. Thus in 

 1897 production in Thompson's Lake (10.41) was 217 percent, 

 in excess of that in the channel (3.28), while in 1898 (5.06 and 

 2.03) the excess was only 149 per cent. In Phelps Lake, on the 

 other hand, production rose to the unparalleled height of 37.34, 

 the mean of the monthly averages, 67 per cent, above the mean 

 of all monthly averages, and fourfold that in the previous year, 

 when the last 4 months were cut off by the drying up of the lake- 



Production in Quiver Lake in this year is 1.96 cm. 3 , mean 

 of monthly averages, or 2.44, average of all collections — 12 per 

 cent, and 44 per cent, above the mean respectively of all years. 

 This larger production is due to the excessive production in the 

 vernal pulses in May and June and to the high levels of pro- 

 duction in November and December, rising 138, 78, 217, and 176 

 per cent, above the average respectively for these months. The 

 hydrographic conditions in these months in Quiver Lake are 

 favorable to increased production. The May and June pulses 

 are at levels (11 ft.) when impounded run-off from slightly 

 submerged bottom-lands to the north was rapidly draining to 

 the channel through the lake. In November and December 

 there was at least double the usual volume of water in the lake, 

 due to a 34 per cent, increase in river levels, with a considera- 

 ble reduction in the proportion of tributary water and increase 

 in the impounding function. In the remaining 8 months of 

 the year, then, average production is 79 per cent, below the 

 general average for those months in Quiver Lake. This very 

 considerable depression in production falls in the main in the 

 period of greatest hydrographic disturbance. This body of 

 water, owing to its frequent invasion by channel waters and to 



