The IDEM Office of Water Quality (OWQ) develops the Indiana 303(d) List of Impaired Waters as part of the state's Integrated Water Monitoring and Assessment Report, which is submitted to the U.S. EPA every two years in accordance with Sections 305(b) and 303(d) of the Clean Water Act (CWA).
CWA Section 305(b) requires states to make water quality assessments and provide water quality reports to the U.S. EPA, and CWA Section 303(d) requires states to identify waters that do not or are not expected to meet applicable state water quality standards with federal technology-based standards alone. Under CWA Section 303(d), states are also required to develop a priority ranking for these waters considering the severity of the pollution and the designated uses of the waters. Once this listing and ranking of impaired waters is completed, states are required to develop Total Maximum Daily Loads (TMDLs) for these waters in order to achieve compliance with the water quality standards.
Indiana’s 2026 303(d) List of Impaired Waters
On February 5, 2026, IDEM published a draft 2026 Section 303(d) List of Impaired Waters for Indiana and Consolidated Assessment and Listing Methodology (CALM) document on the IDEM Integrated Water Monitoring and Assessment Report and Section 303(d) List webpages for a 45-day public comment period. A notice directing the public to the draft 2026 303(d) list and CALM was posted in the Indiana Register on February 25, 2026. The public comment period ended on March 21, 2026, and IDEM received numerous comments from the Indiana citizens.
IDEM uploaded its 2026 Integrated Report, including the finalized 2026 303(d) List of Impaired Waters to U.S. EPA’s Assessment and Total Maximum Daily Load Tracking and Implementation System (ATTAINS) online database on April 1, 2026.
IDEM’s 2026 303(d) List of Impaired Waters Submittal
Appendix H of the 2026 Integrated Water Monitoring and Assessment Report includes the 303(d) List (Category 5 of Indiana’s Consolidated List) and Category 4 waters, which are those that are impaired but do not require a Total Maximum Daily Load. Combined, these categories include all known impairments to Indiana waters:
The Listing Tables include the following information:
- Category 5 of Indiana’s Consolidated Listing of All Waters (the 303(d) List)
- Category 4 of Indiana’s Consolidated Listing of All Waters, which includes impaired waters that do not require a Total Maximum Daily Load (TMDL) under Section 303(d) of the Clean Water Act
- A TMDL Key for the impairments identified in Category 4A
- A change file for Categories 4 and 5, which describes all the modifications made to these lists since IDEM’s 2022 303(d) list was approved by U.S. EPA.
General information on the 303(d) list and files from previous listing cycles are available on the Section 303(d) List Frequently Asked Questions page. You may also contact the Integrated Report Coordinator with any questions you have regarding the 303(d) list.