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Topic
- Water--Pollution 112
- Rivers--Oregon 69
- Lectures and lecturing 20
- Izaak Walton League of America 14
- Sewage disposal plants 14
- Fishes--Conservation 13
- Dams 11
- Salmon 10
- Algae 8
- Willamette River (Or.) 7
- Water quality 6
- American wit and humor, Pictorial 5
- Oregon--Politics and government 5
- United States--Politics and government--1933-1953 5
- United States--Politics and government--Caricatures and cartoons 5
- Wildlife management 5
- Wildlife refuges 5
- World politics--Caricatures and cartoons 5
- Agriculture 4
- Birds--Conservation 4