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Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) is a multipurpose environmental analysis system developed by the U.S. Environmental Protection Agency (EPA) for use by regional, state, and local agencies in performing watershed- and water-quality-based studies.

BASINS was developed primarily to address four objectives: facilitating examination of environmental information, supporting analysis of environmental systems, providing a framework for examining management alternatives, and supporting development of Total Maximum Daily Loads (TMDLs). Through the use of a geographic information system (GIS), BASINS has the flexibility to display and integrate a wide range of information at a scale chosen by the user. Additionally, the customized MapWindow interface allows the user to efficiently access national environmental information, apply assessment and planning tools, and run a variety of proven, robust nonpoint loading and water quality models.

Intended User: BASINS is intended for environmental program managers at the local, state, or regional level.

Geographic focus: Model is designed to simulate any watershed, provided the user selects or enters the appropriate input information.

Scale: From river reach to multi-watershed

Developer: U.S. EPA, contact Lisa Larimer at

  • How are source contributions estimated?
  • What does the user need to input?
  • Considerations