As a part of a more comprehensive investigation of the Yakima River, including physical, chemical and biochemical tests, a biological investigation was made. To determine the effects of pollution and the addition of nutrients to the waters of the Yakima River upon the drifting microscopic plants and animals, three nannoplankton samples were collected and analyzed in the laboratory. Collections of bottom fauna, primarily insects, were made at six stations in the Cle Elum to Kiona reach of the main stem Yakima River on September 14 and 21, 1961. The complete record is presented.