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- Bodies of water 7
- Conservation of natural resources 7
- Northwest, Pacific 7
- Fisheries 4
- Maps 4
- Rivers 4
- Water-power 4
- Wildlife conservation 4
- Agriculture 3
- Hydroelectric power plants 3
- National parks and reserves 3
- Photography 3
- Renewable energy sources 3
- Water resources development 3
- Hydrothermal electric power systems 2
- Industrialization 2
- Irrigation projects 2
- Landscape protection 2
- Recreation 2
- Riparian areas 2
