Prolonged droughts, which have occurred periodically in Colorado, dry out the topsoil, which is the most productive layer. The topsoil is then carried away by the winds that sweep across the plains. Since the 1930s modern farming techniques have been introduced to decrease the destructive effects of soil erosion. Protection of the watersheds, especially in western Colorado, is undertaken by maintaining the plant and tree cover on them. This slows down the rate of runoff and increases the amount of rainwater that eventually finds its way into the groundwater and rivers, and therefore into the water supply.
Wildlife conservation is conducted in the national and state parks and wilderness areas.
Hunting is permitted seasonally, but it is carefully controlled. Fishing is also controlled, and rivers are stocked with fish. The work of protecting the environment in Colorado is done by the state departments of Natural Resources and Health. Divisions within the departments oversee air pollution control, the disposal of hazardous waste, and water quality issues. In 1998 the state had 15 hazardous waste sites on a national priority list for cleanup due to their severity or proximity to people.