During the spring, summer, and fall of 1972 through 1975, the National Eutrophication Survey (NES) sampled 815 lakes throughout the 48 contiguous United States. About 2 1/2-million physical, chemical, and biological measurements were made of the lakes studied. This report, Part I, presents the methodology, rationale, output format, and data limitations of the product. The physical, chemical, and morphometric conditions of the 250 lakes included in the study are described. The mechanics and logic of interfacing physical and chemical data (total phosphorus; orthophosphorus; nitrite-nitrate-, ammonia-, and total Kjeldahl-nitrogen; nitrogen/phosphorus ratio; Secchi disk transparency; chlorophyll a; turbidity; pH; total alkalinity; dissolved oxygen; and temperature) with biological data to establish the environmental requirements and the relative importance of phytoplankton are described.

"March 1979." Includes bibliographical references.

pt. 1. Methods, rationale, and data limitations -- pt. 2. Genera Acanthosphaera through Cystodinium collected from eastern and southeastern lakes -- pt. 3. Genera Dactylococcopsis through Gyrosigma collected from eastern and southeastern lakes -- pt. 4. Genera Hantzschia through Pteromonas collected from eastern and southeastern lakes -- pt. 5. Genera Quadrigula through Zygnema collected from eastern and southeastern lakes -- pt. 6. The common phytoplankton genera from eastern and southeastern lakes -- pt. 7. Comparison of some new and old indices and measurements of trophic state -- pt. 8. Algae associated with or responsible for water-quality problems.