The map layer shows the flowlines of surface water resources in California, including streams, rivers, canals, ditches... etc.
The National Hydrography Dataset is the surface water component of "The National Map".  It contains features such as lakes, ponds, streams, rivers, canals, dams and streamgages. These data are designed to be used in general mapping and in the analysis of surface-water systems. (http://nhd.usgs.gov/)

This map layer limited the dataset to include just the flowlines of streams/rivers, canals/ditches, connectors, and artificial paths in California.  Flowlines which were removed include the coastline and underground pipes.
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