532 



SplKTriuiu, Pisidiiiin, and Ancydus were all abundant, as was also 

 tliunatella rcpcns on sticks and logs. 



In Depue Lake itself dip-nets, dredges, and small seines yielded 

 many common worms not found above, naiids, planarians, etc., and 

 Hyalella knickerbockeri was abundant among algse, in all situations. 

 Insect larvae were likewise present in unusual variety, including 

 Chironomus and Ceratopogon larvae, larvae of caddis-flies and May- 

 flies {Ccenis and Callibcctis), tipulid larvae, and larvae of several 

 species of larger dragon-flies and damsel-flies (Agrionince) . Among 

 the mollusks were Quadntla imdidata, Q. plicata, Vizipara contec- 

 toides, Lioplax, Sphccrium transversiim, and Ancylus, besides a num- 

 ber of species represented only by dead shells. Fishermen believe 

 that the poisonous wastes from the Depue zinc works are killing the 

 shells on the bottom of this lake. It was here that the first com- 

 mercial fisheries were encountered; and a haul made at the foot of 

 Depue Lake October i8, yielded about two hundred pounds of carp 

 and a hundred pounds of sunfish and crappies. 



Hennepin to Henry 



At Hennepin the water became to all appearance practically nor- 

 mal, even in the midsummer of 191 1, being odorless, greenish with 

 phytoplankton, and free from suspended clusters of foul-water or- 

 ganisms and particles of sewage debris. Here we found commercial 

 fii^hinu" in progress in bnth the river and the adjacent lakes, mainly, 

 however, in the latter. Mud taken in September from the bottom 

 of the channel at Hennepin was more sandy than above, had no 

 offensive odor, contained many snails — Campelojiia, Pleiirocera, etc., 

 many specimens of Sphcrriuui transrersuin, and only a moderate num- 

 ber of slime worms. Similar materials were obtained from the bot- 

 tom at the Henry dam, except that the sediments in the sluggish 

 current there were softer, finer, and darker than in the full flow of 

 the stream at Iltnnepin. At the low temperatures of March, 1913, 

 however, the sludge was offensively corrupt much farther down the 

 stream than in the wanner season, as will be more fully explained 

 under the next section. The midsummer microplankton of 191 1 con- 

 firmed the other lines of evidence, yielding but 2 septic organisms to 

 the cubic centimeter as compared with 16 at Starved Rock and 80 

 at Morris; and 6 pollutional forms as compared with 7 at Chilli- 

 cothe below, 71 at Starved Rock, 134 at Marseilles, and 142 at 

 Morris. Fonns classed as contaminate, on the other hand, were 

 more numerous both here and at Chillicothe than above, and clean- 



