antidegradation

Antidegradation programs, a requirement of the Clean Water Act, work to protect existing uses of all surface waters, prevent waters with higher than minimum standards from deteriorating, and maintain and protect waters that are designated as Outstanding Natural Resource Waters (ONRW). Only under certain conditions can the degradation of water quality in high quality waters be allowed. States/tribes must have both an antidegradation policy and an implementation plan.

Click here for more information from the US EPA: http://water.epa.gov/scitech/swguidance/standards/adeg.cfm