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Over the past two decades, evaluations of available water-quality information have led to the conclusion that the United States needs long-term water-quality assessment to support water policy and management. The National Water-Quality Assessment (NAWQA) program of the U.S. Geological Survey (USGS) is designed to describe the status and trends in the quality of the Nation's ground water and surface water resources. It aims to link assessment of status and trends with an understanding of the natural and human factors that affect water quality.

The NAWQA program is divided into 59 study units located throughout the United States. The study units are delimited by major hydrological systems that are geographically defined by ground- and surface-water features. The study units are divided into three groups, which are intensively studied on a rotational schedule. The first cycle of assessment for each group of study units consists of 2 years of initial planning and retrospective analysis of existing data, 3 years of intensive data collection and analysis, and 6 years of report preparation and low-level assessment activity.

The Lower Illinois River Basin (LIRB) was selected as one of the second set of study units. The LIRB study began in 1994. The components that are studied are ground water, surface water, ecology, and bed sediment and fish tissue. Each component has unique strengths and weaknesses for assessing characteristics that are related to water-quality conditions, and each requires a unique sampling design. The LIRB study unit has finished the high-intensity phase of sampling and currently is in the report-writing phase. The report-writing phase will continue through 2001.