The Altered Watercourse Project was a joint effort between the Minnesota Pollution Control Agency (MPCA) and Minnesota Geospatial Information Office (MnGeo) to create a statewide inventory of streams that have been hydrologically altered (e.g. channelized, ditched or impounded). The dataset was created to support MPCA's water quality monitoring and assessment program and provides information about stream habitats that have been compromised through such alteration. The project entailed digitization of Geographic Information System (GIS) 'events' on to the United States Geological Survey's National Hydrography Dataset (NHD) stream linework. The events were then categorized as one of four types: Altered, Natural, Impounded, or No definable channel, based upon a standardized methodology and criteria. These categorizations were performed manually by GIS technicians using visible interpretation of multiple years of aerial photography, LiDAR (Light Detection And Ranging)-based elevation data, and various other reference data in ArcGIS 10.0. Beginning in 2018, some custom linework was added to the dataset to represent streams that were not present in the NHD. These custom line features do not have a Reachcode, and have a note in the Permanent ID field and the Source Feature ID. These line features will be incorporated into the NHD in the future.