Ecological problems

Man has exploited nature during the 19th and 20th centuries. Therefore, in America he has changed many productive Indian systems of life: the Oklahoma plains of the Kiow, rich in grass and buffalo, into a dust bowl; the Washington salmon streams of the Haida into a sequence of DDT-poisoned reservoirs; the British Columbian Kootenay Lake of the Tlinglit, filled with fish, into a recipient for fertilizers.