EPA Documents for the Arizona Section 303(d) List

The Clean Water Act (CWA) requires each state identify those waters within its boundaries that do not meet applicable state water quality standards. This list is referred to as the Section 303(d) List of Impaired Waters and is approved or disapproved by EPA.

On June 16, 2022, EPA issued its decision to partially approve and partially disapprove Arizona’s 2020 List of Impaired Waters. EPA found Arizona’s decision not to list two waters was inconsistent with the provisions of Arizona’s water quality standards for methylmercury in fish tissue. These criteria are designed to protect the public from exposure to harmful levels mercury when consuming fish from Arizona waterways. EPA has identified Horsethief Lake (Yavapai County) and Santa Fe Lake (Coconino County) as impaired by methylmercury in fish tissue and as requiring Total Maximum Daily Loads (TMDLs) under Clean Water Act, Section 303(d).

• EPA Letter: Arizona’s 2020-2022 List of Impaired Waters under Clean Water Act (CWA) section 303(d) (2020-2022 List) (pdf) (June 16, 2022)
  EPA's letter to Arizona Department of Environmental Quality partial approval of Arizona’s 2020-2022 List of Impaired Waters under Clean Water Act (CWA) section 303(d) (2020-2022 List).
• EPA Letter to Arizona Department of Environmental Quality (pdf) (9/14/2018)
  EPA's letter to the Arizona Department of Environmental Quality regarding Arizona 2018 Clean Water Act Section 303(d) List of Impaired Waters.
• Enclosure: EPA's Review of Arizona’s 2018 Section 303(d) List (pdf) (9/14/2018)
  EPA's rationale for EPA's approval of Arizona’s 2018 list of water quality limited segments requiring a Total Maximum Daily Load (TMDL) under Clean Water Act, Section 303(d).