This dataset contains phytoplankton data from Oneida Lake from 1975 to present and is part of the collection Cornell Oneida Lake Data. The Cornell Biological Field Station (CBFS) serves as a primary field site for aquatic research at Cornell University (more information can be found at http://cbfs.dnr.cornell.edu/index.html) and is part of the Department of Natural Resources, College of Agriculture and Life Sciences ,Cornell University. The centerpiece of the station's research program is a 60-year database on the food web of Oneida Lake, New York, that has been collected with support from the Cornell University Brown Endowment and from the New York State Department of Environmental Conservation. The data are collected by personnel from the Cornell Biological Field Station and include limnology, benthos, zooplankton, phytoplankton, and fish survey data, primarily from Oneida Lake and spanning 1957 to the present. This data package contains results of phytoplankton surveys of Oneida Lake, New York divided in two series: 1975 - 1995 and 1996 to present. The primary tables give densities of phytoplankton taxa identified in samples collected from sites in Oneida Lake. Five of these sites are standard sites and used when stations are pooled. A derived table has the densities and biovolumes of each taxa averaged over the five standard stations (1975 to 1995 data). Supplemental tables provide explanations of the taxonomic codes used in the two primary tables as well as geographic coordinates and information for the sampling sites.