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- Rivers 129
- Bodies of water 36
- River engineering 33
- United States. Congress--Records and correspondence 32
- River surveys 31
- Politics and government 24
- River channels 23
- Irrigation 22
- Northwest, Pacific 22
- Harbors 21
- Agriculture 20
- Economics 18
- Hydrology 18
- Dams 17
- Canals 16
- Watersheds 16
- West (U.S.) 15
- Rapids 13
- Water quality 13
- Technology 11