Delaware.gov logo

Total Maximum Daily Loads



When monitoring reveals that waterways do not meet Delaware’s water quality standards, they are reported on a list of impaired waterways (303(d) List). For each impaired waterway, the Federal Clean Water Act (CWA) requires states to develop Total Maximum Daily Loads (TMDLs) for the pollutants of concern. A TMDL sets a limit on the amount of pollution that can be discharged into a waterbody such that water quality standards can still be met. A non-scientific definition for TMDL could be “pollution limit.”

Pollutants in Delaware waters are often chemicals, such as nitrogen and phosphorus from fertilizer runoff and wastewater, but TMDLs could also be set for other pollutants such as bacteria, sediments, or even heat – anything that can injure a waterway’s natural health. Pollutants can come from specific point sources or from nonpoint sources. Point sources are discrete sources of pollution, and include facilities that have a National Pollution Discharge Elimination System (NPDES) Permit, such as municipal and industrial wastewater treatment plants.

Nonpoint source pollution travels over and through the ground from many diffuse sources, including human activities on agriculture and developed lands like septic systems and runoff from lawns, farms, parking lots, and golf courses.

TMDLs consist of three parts: a wasteload allocation (WLA) for point sources, a load allocation (LA) for nonpoint sources, and a margin of safety (MOS): TMDL = WLA + LA + MOS

TMDLs by Watershed

Delaware has been establishing TMDLs for our State’s impaired waters since 1998. Monitoring and other types of data are used to develop models that can predict how water quality will change under a variety of pollutant loading scenarios. These models help us determine TMDL levels that will achieve water quality standards.

The tables below list all of the TMDLs that have been established in Delaware and provides links to technical analysis documents and the resulting regulations.

Each tab includes the watersheds in a major drainage area. Each watershed listed is numbered and shown on the map on this page.

In addition, Maps 2, 3, and 4 at the bottom of the page are provided to show reductions in nonpoint source nitrogen, phosphorus, and bacteria loads as required by the TMDLs in order to achieve water quality goals.

Watershed Developed by Year Analysis Documents Regulations
Naamans Creek (1) DNREC 2005 Nutrients and Bacteria Nutrients and Bacteria
Shellpot Creek (2) DNREC 2005 Nutrients and Bacteria Nutrients and Bacteria
Brandywine Creek (3), Red Clay Creek (4), White Clay Creek (5), and Christina River (6) EPA Revised 2006
2006
Revised 2006
High-Flow Nutrients
High-Flow Bacteria
Low-Flow Nutrients
Red Clay Creek (4) DNREC 1999, Amended 2009 Zinc Zinc
White Clay Creek (5) DNREC 1999 Zinc Zinc
Watershed Developed by Year Analysis Documents Regulations
Army Creek (8) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Red Lion Creek (9) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Dragon Run Creek (10) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
C&D Canal East and Lums Pond (11) DNREC 2012 Nutrients Nutrients
Appoquinimink River (12) EPA
DNREC
2003
2006
Nutrients
Bacteria
Bacteria
Blackbird Creek (13) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Smyrna River (15) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Leipsic River (16) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Little Creek (17) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
St. Jones River (18) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Murderkill River (19) DNREC
DNREC
2014 Amended
2006
Nutrients
Bacteria
Nutrients
Bacteria
Mispillion River (20) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Cedar Creek (21) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Broadkill River (22) DNREC 2006 Nutrients and Bacteria Nutrients and Bacteria
Delaware Estuary Zones 2-5 EPA 2003 PCBs
Delaware Estuary Zone 6 EPA 2006 PCBs
Watershed Developed by Year Analysis Documents Regulations
Chester River (28), Choptank River (29), Marshyhope Creek (30), Nanticoke River (31), Gum Branch (32), Gravelly Branch (33), Deep Creek (34), Broad Creek (35), and Pocomoke River (37) DNREC 2006 Bacteria Bacteria
Chester River (28) DNREC 2005 Nutrients Nutrients
Choptank River (29) DNREC 2005 Nutrients Nutrients
Marshyhope Creek (30) DNREC 2005 Nutrients Nutrients
Nanticoke River (31), Gum Branch (32), Gravelly Branch (33), Deep Creek (34), and Broad Creek (35) DNREC 1998
2000
Nutrients in the mainstem of the Nanticoke River and Broad Creek
Nutrients in the tributaries and ponds of the Nanticoke River and Broad Creek
Pocomoke River (37) DNREC 2005 Nutrients Nutrients
Watershed Developed by Year Analysis Documents Regulations
Lewes-Rehoboth Canal (38), Rehoboth Bay (39), Indian River (40), Iron Branch (41), Indian River Bay (42), Buntings Branch (43), Assawoman Bay (44), and Little Assawoman Bay (45)  DNREC 2006 Bacteria Bacteria
Lewes-Rehoboth Canal (38), Rehoboth Bay (39), Indian River (40), Iron Branch (41), and Indian River Bay (42)  DNREC 1998 Nutrients Nutrients
Little Assawoman Bay (45) DNREC 2005 Nutrients Nutrients
Indian River (40) EPA 2004 Temperature
Buntings Branch (43) DNREC 2004 Nutrients

Setting pollution limits is just the first step toward improving water quality.  Once the pollutant limits are established, efforts must be taken to reduce the pollutant loads from point and nonpoint sources. The Watershed Assessment Section works with Tributary Action Teams to identify voluntary and regulatory actions for each impaired region of the state. Collectively, these actions are called pollution control strategies (PCS) and they are designed to achieve TMDLs and water quality standards. In addition, other types of watershed plans and strategies have also been developed across the state.




+