A survey of four lakes (Coose, Big, Sand, and Mud) on the floodplain of the Mississippi River near Quincy, in Adams County, Illinois, was conducted from August, 1949, to July, 1952, to study seasonal and annual variations in the plankton and the bottom fauna in relation to environmental factors. All of the lakes included in this study occupied meander depressions formed by stream action on the floodplain. This is clearly shown in an aerial photo map of part of the South Quincy Drainage District (fig. 1). This map shows three of the lakes studied, as well as other bodies of water occupying parts of an old stream channel. Differences in natural and cultivated vegetation and in soil structure indicate former limits of the old channel, only a small part of which was occupied with water. The lakes were very shallow, and the bottom, when exposed, presented a saucer-like form. They were of relatively uniform depth, and there were no deep parts. Any depression, such as that created by dredging, was soon obliterated by wave action which drifted bottom materials into the depression and filled it. Finch and Trewartha ('1936) have described the physiographic changes occurring as a result of stream action on a valley floor.