Columbia subject headings:
Harvard subject headings:
Natural history--Superior, Lake.
Superior, Lake--Description and travel.
Superior, Lake--History.
Water quality--Superior, Lake.
Water--Pollution--Superior, Lake.
Princeton subject headings:
Ecology--Superior, Lake.
Environmental protection--Superior, Lake--History.
Lake conservation--Superior, Lake--History.
Natural history--Superior, Lake Region.
Pollution--Superior, Lake--History.
Superior, Lake--Description and travel.
Superior, Lake--Environmental conditions--History.
Superior, Lake--History.
Water quality--Superior, Lake.
Water--Pollution--Superior, Lake.