443 
ters very largely independent of backwaters and tributaries by 
reason of cutting off of communication in some cases and ces- 
sation of run-off in others. Along with this independence goes 
increased fertility by virtue of greater relative contamination 
by sewage and longer time for breeding by reason of the slack- 
ened current. Asa result, production in channel waters reach- 
es in July-November, 1897, a level unsurpassed in our records, 
rising above the monthly means of all years (see table fol- 
lowing page 342) 11 per cent. in July, 245 per cent. in Sep- 
tember, 250 per cent. in October, and 14 per cent. in Novem- 
ber, but falling behind by 6 per cent. in August. As a result of 
this increased development of plankton in the channel the pro- 
duction in backwaters becomes relatively less with respect to 
the channel production than in times of high water. Thus in 
‘July-December, backwater plankton exceeds that in the chan- 
nel in only 10 out of 19 monthly averages, or, omitting Spoon 
River, in 8 out of 15—a marked change from the excess in the 
preceding six months, 21 out of 25. 
This is the only season in all our records in which the plank- 
ton content of Spoon River rises above the barren level of .1 
em.* per m.’, or less. The production now rises to a level ap- 
proximating, and in November-December exceeding, that in 
the channel asa result of the practical absence of current and 
consequent increase in the reservoir function of the stream. 
The course of production this year in the various backwa- 
ters is in most instances strikingly similar to that in the chan- 
nel in its major outlines. Thus in all of them (Pl. XXVIIL, 
XXXIL, XXXIV., XXXVIII., and XLI.) production rises grad- 
ually from the midwinter minimum to an unusually low ver- 
nal pulse in April-May and declines again in June-July. At 
this point collections were suspended in Dogfish and Flag lakes. 
Production in channel waters rises again in August and con- 
tinues at high levels till November, and in like manner and 
with even greater amplitude in Thompson’s Lake (Pl. XXX- 
VIUI.), while a similar movement is initiated in Phelps Lake 
(Pl. XLI.), only to be stopped by the drying up of the lake in 
