What is an Outstanding Arizona Water (OAW)? 

An OAW is a special designation given to high-quality waters that have exceptional recreational or ecological significance or that support threatened or endangered species. Existing water quality on OAWs must be maintained with the exception of temporary impacts, such as maintenance on a bridge crossing the water.

The Clean Water Act (CWA), specifically under § 303(c), as implemented by 40 CFR 131.12, requires states to adopt and implement an antidegradation policy to provide enhanced protection of surface water quality. Arizona’s program can be found in the Arizona Administrative Code (A.A.C.) Title 18, Chapter 11, Article 107 (R18-11-107). 

Arizona currently has 22 designated OAWs | View PDF >

What is Antidegradation?

Antidegradation policies are designed to prevent the lowering of water quality in surface waters so they can remain usable for drinking water, aquatic life, and recreation activities. There are three tiers of protection: 

• Tier 1 | Surface water quality must meet the standards of the designated use(s) and shall be maintained and protected
• Tier 2 | Surface water quality is better than the standards applied to the designated use(s), but the lowering of water quality may be permitted if deemed necessary while still meeting standards.
• Tier 3 |  Surface water quality is as good or better than the standards applied to the designated use(s) and shall be maintained, protected and cannot be degraded. 

At the federal level, Tier 3 waters are called Outstanding Natural Resources Waters (ONRWs); in Arizona, they are known as OAWs. While every state must have an ONRW program, the designation of specific waters is optional. 

How does a surface water become an OAW?

A surface water must meet criteria outlined in the Arizona Administrative Code (A.A.C.)¹, including: 

• Flow conditions
• Water quality (at least meets current water quality standards)
• Ecological or recreational significance
• Supports endangered or threatened species

ADEQ must evaluate and consider the criteria outlined in A.A.C. R18-11-112(D) | View A.A.C. >  

What surface waters are eligible for OAW designation?

An OAW must be a perennial or intermittent water that is free-flowing and meets all applicable surface water quality standards and:

• is of exceptional recreational or ecological significance because of its unique attributes, such as the geology, flora and fauna, water quality, aesthetic value, or the wilderness characteristic of the surface water; or
• if an endangered or threatened species is associated with the surface water and the existing water quality is essential to the species' survival. 

How does OAW Designation protect surface waters?

Once designated as an OAW, its water quality must be maintained at the level it had at the time of designation. In other words, even slight decreases in water quality are not permitted — high water quality must be preserved.

The designation adds additional regulatory measures to prevent the water quality from degrading due to point source discharges, such as those regulated under the National Pollutant Discharge Elimination System (NPDES/AZPDES) permits. This includes:

• New or increased dischargers directly to OAWs are prohibited unless they meet strict regulatory exemptions as outlined in A.A.C. R18-11-107.01(C)(2). 
• While there are currently no regulatory measures to control nonpoint source pollution, ADEQ works collaboratively with landowners, land managers, and other stakeholders to protect and enhance surface water quality | See More >

¹A.A.C. R18-11-112(C) | View >