Section 305(b) of the Federal Clean Water Act requires that states and other entities prepare and submit Watershed Assessment Reports to the US EPA on April 1 of every even-numbered year. The 305(b) reports and monitoring data are used to compile a list of impaired waters, commonly referred to as the 303(d) list.

The EPA summarizes these reports and prepares a report of their own to Congress.

For more information, please contact the Watershed Assessment and Management Section at 302-739-9939.

Water Quality Standards and Impaired Waters

Impaired waters are polluted waters. They are waters that do not meet water quality standards for their designated uses, such as recreation, fishing, or drinking.

Impaired waters could be suffering from excess nutrients, low dissolved oxygen, toxins, bacteria, heat, or any combination of these problems. The most common causes are pathogens, such as bacteria, and nutrients, especially nitrogen and phosphorus. Because most impairments come from nonpoint sources, they are harder to control.

When waters are identified as impaired on 303(d) lists, a Total Maximum Daily Load (TMDL) must be developed.

Tributary Action Teams and other groups may recommend pollution control strategies and other types of watershed plans to improve the quality of our waterways.

Related Links

Whole Basin Management

Total Maximum Daily Loads (TMDL)

External Data Policy

Delaware’s Integrated Report

The Combined Watershed Assessment Report (305(b)) and Determination for the Clean Water Act Section 303(d) List of Waters Needing TMDLs, commonly called the “Integrated Report,” is published every two years.

The DNREC Watershed Assessment Section actively solicits information from a wide variety of sources and evaluates the information for inclusion in 305(b) reports. If you have or know of information that should be used in the preparation of the report or the 303(d) list, please contact the section.

2026 State of Delaware Integrated 305(b)-303(d) Report

Final Integrated Report (PDF)

• ATTAINS Summary (EXCEL)
• Parameter Tables (EXCEL)
• Summary Tables (EXCEL)

2024 State of Delaware Integrated 305(b)-303(d) Report

Final Integrated Report (PDF)

• ATTAINS Summary (EXCEL)
• Parameter Tables (EXCEL)
• Summary Tables (EXCEL)

Earlier Integrated Reports

Related Topics:  303(d), 305(b), assessment, clean water, clean water act, water quality, watershed, watershed stewardship