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.