In the early years of the twentieth century (the Progressive Era),
conservation came to mean scientific and rational planning for the
efficient use of natural resources. Scientists working for the
federal government developed and promoted conservation.
The term conservation first applied to
water resources. Much of the western United States was arid, and hydrologists
and other scientists working for the federal government developed the
idea of impounding spring floods begin dams so that the water could be
used year-round for irrigation and other purposes.
The use of the word "conservation" to apply to water resources soon spread to
include all natural resources.