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- Agriculture 2
- Bodies of water 2
- Conservation of natural resources 2
- Fisheries 2
- Irrigation projects 2
- Northwest, Pacific 2
- Renewable energy sources 2
- Wildlife conservation 2
- Environmental impact analysis 1
- Flood control 1
- Forests and forestry 1
- Hydraulic engineering 1
- Hydroelectric power plants 1
- Hydrothermal electric power systems 1
- Maps 1
- Mineral industries 1
- National parks and reserves 1
- Photography 1
- Pumped storage power plants 1
- Recreation 1
