History 45 Water quality management 14 Planning 13 Politics and government 13 Pollution 13 Water 12 Economic conditions 11 lisää ... History and criticism 11 Environmental aspects 10 World War, 1939-1945 10 Civil rights 9 Law and legislation 9 Statistics 9 Housing 8 Population 8 Social aspects 8 Land use 7 Social life and customs 7 African Americans 6 Economic policy 6 Foreign relations 6 Histoire 6 Bibliography 5 Census, 1990 5 Criticism and interpretation 5 Economic aspects 5 Environmental policy 5 Mexican Americans 5 Prevention 5 Research 5 vähemmän ...