Antidegradation

To protect the existing uses of waters, and to protect waters with water quality levels better than necessary to support propagation of fish, shellfish and wildlife, and recreation in and on waters of the states, a set of policies called "antidegradation" comes into play. The purpose of these policies is to keep clean waters clean. States, tribes, and territories usually cover this program as part of their water quality standards regulations.

Antidegradation is generally considered to have three components, or "tiers" of protection: (1) protection and maintenance of existing uses of waters, (2) protection of high quality waters, and (3) outstanding national resource waters.