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- Bodies of water 7
- Northwest, Pacific 7
- Rivers 4
- Aerial photographs 3
- Conservation of natural resources 3
- Hydroelectric power plants 3
- Renewable energy sources 3
- Water-power 3
- Dams 2
- Fisheries 2
- Hydrothermal electric power systems 2
- Photography 2
- Pumped storage power plants 2
- Wildlife conservation 2
- Agriculture 1
- Electric power production 1
- Environmental impact analysis 1
- Flood control 1
- Hydraulic engineering 1
- Industrialization 1