EPA Documents for the Arizona Section 303(d) List of Impaired Waters

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 May 24, 2024, EPA issued its decision to partially approve and partially disapprove Arizona’s 2024 List of Impaired Waters. EPA found Arizona’s decision not to Patagonia Lake 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 Patagonia Lake (Santa Cruz) as impaired by methylmercury in fish tissue and as requiring Total Maximum Daily Loads (TMDLs) under Clean Water Act, Section 303(d).

EPA is soliciting public comments through July 5, 2024, on the addition of Patagonia Lake as impaired by methylmercury in fish tissue. After considering public comments and making any revisions EPA deems appropriate, EPA will transmit the listing to Arizona.

Documents

• EPA Letter: Arizona’s 2024 List of Impaired Waters under Clean Water Act (CWA) Section 303(d) (2024 List) (pdf) (423.48 KB, May 24, 2024)
  EPA’s letter to Arizona Department of Environmental Quality partial approval of Arizona’s 2024 List of Impaired Waters under CWA Section 303(d) (2024 List).
• Arizona’s 2024 Integrated Report (pdf)
• Arizona’s 2024 Integrated Report Appendices (xlsx)

Prior Actions

• EPA Letter: Arizona’s 2020-2022 List of Impaired Waters under Clean Water Act (CWA) section 303(d) (2020-2022 List) (pdf) (264.23 KB, 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) (666.59 KB, 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) (488.9 KB, 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).