3Gr 



figures than at the Narrows continued in mid-channel to and below 

 the foot of the lake. But in the first week of August 1920 the bottom 

 oxygen dropped sharply below the Narrows from a high figure for 

 the season of 6.4 p. p. m. to only 3.4 a mile below, and to 2.0 p. p. m. 

 opposite Green Street, which is a mile above the foot of the lake. On 

 the same dates a rapid rise in bottom oxygen figures from the channel 

 eastward into the wide waters was noted a mile below the Narrows ; 

 but opposite Green Street samples showed between three and two 

 parts per million for two fifths of a mile eastward into the open lake. 



Bottom Dissolved O.xygen, Mio-C'HA.\Ntx, Loweu Peouia Lake, 1920-1922 

 Midsummer Figures, Parts per Million — Averages 



' Milt'S below Lake Michigan. 



Small Bottom Animals 



In the two lower lake cross-sections of 1922 and tb.ose in the river 

 immediately adjoining, there were taken in all 28 species of small 

 bottom invertebrates, or 5 more than the total taken in the middle lake 

 the same season and 9 more than the total from the upper. Worms, 

 leeches, midges, and Musculium transversum accounted, for 17 of the 

 total of 28 species; the remaining 11 being distributed between the 

 less tolerant snails, in the lower lake reduced to four kinds ; and a 

 miscellaneous group of seven species of Bryozoa, sponges, snails, in- 

 sects, and Crustacea, all of which had their first occurrence both in 

 1922 and 1920 in or below Peoria Narrows. 



The two main features distinguishing the 1922 lower lake fauna 

 from that of the middle lake (Table on p. 3G9) were the reduction in 



