The Eastern Lake Survey-Phase I (ELS-I), conducted in the fall of 1984, was the first part of a long-term effort by the U.S. Environmental Protection Agency known as the National Surface Water Survey. It was designed to synoptically quantify the surface water quality of the United States in areas expected to exhibit low buffering capacity. This effort was in support of the National Acid Deposition Assessment Program. The Survey involved a three-month field effort in which 1612 probability sample lakes and 186 special interest lakes in the northeast, southeast, and upper midwest regions of the United States were sampled. The data base supporting this effort was designed and data management was implemented by the Environmental Sciences Division of the Oak Ridge National Laboratory. This document provides the information necessary for researchers to transfer the ELS-I data base accurately to their own computer systems. A data dictionary, this document also includes complete descriptions of the variables in the data base and of the data set formats.