450 
This is the largest production for this period of the year in our 
records, exceeding the average, .24 em.’, by 75 per cent. and ap- 
proximating or exceeding the monthly average in each instance. 
The cause is to be found in the relatively stable conditions at a 
level sufficient to prevent sewage stagnation beneath the ice- 
sheet which covered the stream prior to the March flood. 
Spoon River continued to discharge barren waters (ay. .011 
em.*), while the backwaters, with the exception of Quiver and 
Thompson’s lakes in March, produced a more abundant plank- 
ton than the channel. Quiver Lake produces .66 cm.’,—an ex- 
cess of 20 per cent. above the usual production for this season, 
and in the first two months has 2- to 3- fold the usual plankton 
content as a result of the moderate levels which make the lake 
a reservoir without greatly increasing its current. When, how- 
ever, the general current of overflow passes through it with the 
March flood, production drops to one fifth of the mean for that 
month. In Thompson’s Lake the mean production is 1.15 em.’, 
56 per cent. below the mean production for these months. It 
also falls below in January and March, when hydrographic con- 
ditions are such (Pl. XX XIX.) that channel water is diverted 
through it, and rises above the mean by 25 per cent. in Febru- 
ary, when the run-off is diminished by falling levels. In Phelps 
Lake the mean production, 3.74 cm.’, is 23 per cent. below the 
mean for these months. This lowered production, which also 
falls below the mean in the last two months, is due, in part at 
least, to the invasion of Spoon River water with the higher 
levels. 
The various years of our operations may be briefly charac- 
terized as follows. 
1894. A year of low water and fairly stable hydrographic 
conditions, with nearly average production in channel and open 
backwaters and deficiency in the vegetation-rich Quiver Lake 
in the months of our records. 
1895. <A year of continued and butslightly interrupted low 
water, with stagnation destroying the winter plankton and 
tending to abnormal production in early summer in channel 
