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- Lectures and lecturing 255
- Rivers--Oregon 151
- Dams 137
- Agriculture 109
- Politics and government 99
- Irrigation 94
- Finance 83
- Water--Pollution 64
- Bureaucracy 58
- Salmon 55
- Technology 52
- Economics 50
- Water consumption 48
- Wildlife refuges 47
- Water quality 44
- Fishes--Conservation 40
- Groundwater 39
- Building 38
- Birds--Conservation 37
- Izaak Walton League of America 34