The purpose of quality assurance/quality control (QA/QC) is to ensure that data from research and monitoring studies are of known and documented quality to satisfy project objectives. QA/QC was an integral and important part for all of the U.S. EPA Aquatic Effects Research Program (AERP) projects. The Watershed Manipulation Project (WMP) was designed to test specific hypotheses relating various watershed process responses to acidic deposition at a variety of temporal and spatial scales through an interdisciplinary research approach. To ensure that data from the various laboratory, plot, hillslope and catchment studies satisfied the WMP objectives, a QA Plan was required that integrated QA/QC activities across all studies. The document describes the integrated approach to the QA program for the WMP and was used to provide QA/QC guidance for all personnel associated with the WMP. It is intended to supplement the Watershed Manipulation Project: Field Implementation Plan for 1990-1992.