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- Locks (Hydraulic engineering) 6
- Northwest, Pacific 5
- Bodies of water 4
- Photography 4
- Rivers 4
- Steamboats 3
- Mountains 2
- Postcards 2
- Riparian areas 2
- Agriculture 1
- Canals 1
- Canals--Design and construction--Costs 1
- Dams 1
- Hydroelectric power plants 1
- Industrialization 1
- Irrigation 1
- Maps 1
- Public utilities 1
- Rapids 1
- Transportation 1