Biological samples were collected at weekly intervals at Council Bluffs, Omaha, Yankton, below Fort Randall Dam, Fort Randall Reservoir, Chamberlain, Mandan, below Garrison Dam, and Garrison Reservoir. At Pierre, Mobridge, and above Garrison Reservoir sampling was monthly or semimonthly. Laboratory chemical analyses were performed on biweekly samples at all stations except above Garrison Reservoir, where they were at monthly intervals. No laboratory chemical tests were run at Mobridge, and total phosphorous and organic nitrogen analyses were not performed at Omaha. Due to the late start of the sampling program (October 1954), the Council Bluffs data are represented only by plankton records.