. Bulletin. Natural history; Natural history. JAN FEB MAR APR MAY JUL AUG SEP OCT NOV DEC Fig. 6.—Seasonal fluctuations of Illinois River water levels at Havana, 1938, 1939 and 1940. Scale in feet. The river levels at Havana, midway between the La Grange and Peoria dams, apparently were little affected by these dams. On either side of the river channel, from De Pue to Meredosia, numerous flu- viatile lakes, ranging in size from 60 to 6,500 acres, dot the bottomlands, fig. 1. Together these lakes form at low stage about 56,000 acres of water surface, while the river channel covers an additional
. Bulletin. Natural history; Natural history. JAN FEB MAR APR MAY JUL AUG SEP OCT NOV DEC Fig. 6.—Seasonal fluctuations of Illinois River water levels at Havana, 1938, 1939 and 1940. Scale in feet. The river levels at Havana, midway between the La Grange and Peoria dams, apparently were little affected by these dams. On either side of the river channel, from De Pue to Meredosia, numerous flu- viatile lakes, ranging in size from 60 to 6,500 acres, dot the bottomlands, fig. 1. Together these lakes form at low stage about 56,000 acres of water surface, while the river channel covers an additional 15,000 acres. In relation to vegetation, lakes in the Illinois River valley may read- ily be grouped under three major types: (1) those with stable waters, except dur- ing flood stages; (2) those with fairly stable water levels, in which the water is high during flood times but is more or less retained during drought periods; and (3) those with widely fluctuating water levels, in which the water rises and falls with that of the river. The lakes of the last type usually have a wide entrance connecting the lower end of the lake with the river, while the land separating lake from river is low and flat, hg. 8. Prior to 1940, lakes with stabilized water levels covered approximately 5,680 acres between Ottawa and Meredosia. These included the Starved Rock Pool, formed by a navigation dam on the Illi- nois River below Ottawa; the remnant of Spring Lake, inclosed by levees within the Spring Lake Drainage District near Ban- ner ; and Lake Chautauqua, an abandoned drainage district above Havana. Prior to 1940, lakes with semistabilized water levels covered about 7,920 acres ad- ILLINOIS RIVER 1939 UAKE CHAUTAUQUA 1939 LAKE CHAUTAUQUA 1940. JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC Fig. 7.—Water levels, in feet, of the Illinois River in 1939 and of Lake Chautauqua in 1939 and 1940. While water levels of the river fluctuate considerably, a stabilized water level is main- tained
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