2028 303(d) Listing Methodology
The Federal Clean Water Act requires Colorado to create a list of waterbodies that do not meet water quality standards. These waterbodies, called “impaired waterbodies,” are added to the 303(d) List of Impaired Waters, also referred to as Regulation 93. The commission will establish the 303(d) List of Impaired Waters at a rulemaking hearing scheduled for February 2026.
The Water Quality Control Division uses the 303(d) Listing Methodology to evaluate whether waterbodies across Colorado meet water quality standards and support their designated uses, such as agriculture, wildlife habitat, recreation, and drinking water. The Water Quality Control Commission will revise the 303(d) Listing Methodology at an administrative hearing scheduled for March 9, 2026.
Due to the anticipated scheduling of the Regulation #93 South Platte Basin rulemaking hearing for February 2026, which will cause resource constraints, the division is proposing limited revisions during this cycle. Revisions will focus on schedule modifications and making the 303(d) Listing Methodology accessible.
How to get involved
The division is holding a 303(d) Listing Methodology stakeholder meeting on Tuesday, Sept. 23, 2025, from 2 to 3:30 p.m. To join the meeting, please register to attend on Zoom. Once the meeting concludes, a copy of the meeting recording, presentation, and other meeting materials will be stored in this public folder. Please sign up to receive notifications about this effort.
For more information about the 303(d) Listing Methodology, please contact:
- Robert Hillegas, at robert.hillegas@state.co.us.
- Skip Feeney, at skip.feeney@state.co.us.