The objectives of this study were: (a) comparison of the qualitative and quantitative aspects of the separate rotifer faunas in each of the discrete lotic and lentic habitats of the Ocqueoc River system; (b) analysis of the differential effects of stream and impoundment conditions, natural or otherwise, on both autochthonous and allochthonous rotiferan faunas; and (c) determination of those factors, whether physical, chemical, biological or combinations thereof, which might be responsible for the development and maintenance of any autochthonous rotifer fauna in the system. This investigation was carried on from 1952 through the summer of 1955. Both living and preserved plankton samples were examined and preserved samples totaled 534 from 42 field stations throughout the system. Quantitative samples were obtained from all significant lakes and from 23 stations in the river. The Lake Nettie and Ocqueoc Lake areas were sites of more detailed study. Selected physico-chemical data were taken simultaneously with plankton collections. Lakes and artificial impoundments of the system were the major locations of plankton development. Lotic situations did not possess a planktonic rotifer fauna distinct from the lakes. Rather, most of the plankton was derived from the lakes, decreased in quantity downstream from the lakes and eventually disappeared. The rate of removal of the plankton was related to length of stream segment, current, depth of water, turbulence, and amount of vegetation or other objects in the channel which supported a periphyton asemblage. The vegetation and periphyton exerted a pronounced filtering effect on the plankton and very little was transported from one lake to another by the river. 24 genera containing 34 species of rotifers were identified in the plankton. The majority of them have been reported in studies of other lakes and rivers. The rotifer fauna varied somewhat from lake to lake, but the variation was more quantitative than qualitative in nature. Within a single lake considerable quantitative variation also occurred. The largest number of species was present in Lake Nettie but the total population there was not the largest within the system. Ocqueoc Lake produced the greatest quantity of plankton. Males of Keratella cochlearis were present in autumn collections from Lake Nettie and Ocqueoc Lake and in summer collections of Moore’s Lake. The unusual presence of males in summer collections has been related not to temperature, but to abundance and quality of food material and to conditions of crowding within Moore’s Lake. Limnias ceratophylli was found as a member of the plankton in considerable numbers in a few lakes of the central alke region. It has previously been regarded as a sessile species and is not usually found as a member of the plankton community. The genus Brachionus was virtually absent from the entire system in spite of the alkaline character of the water. Keratella, Polyarthra and Synchaeta were the genera occurring in greatest abundance during most of the year and throughout most of the system. Keratella cochlearis was the dominant species for the system, both in abundance and distribution.