Aquatic Life Designated Use Project
Introduction: Dissolved Oxygen in the Delaware River Estuary
The Delaware River and the Ben Franklin Bridge, Philadelphia, Pa. Photo by the DRBC.
The Delaware River and the Ben Franklin Bridge,
Philadelphia, Pa. Photo by the DRBC.


Historical Conditions

When the DRBC was created in 1961, little or no dissolved oxygen (DO) was present in the Delaware River Estuary from Wilmington to Philadelphia for periods of up to six months each year.

To combat this serious challenge, DRBC in 1967 established designated aquatic life uses and associated numerical water quality criteria necessary to protect those uses.

The aquatic life designated use in this part of the estuary was set as "maintenance" (survival) of resident fish and movement of migratory fish through these waters to and from spawning areas.

Significant improvements in DO levels have occurred throughout this stretch of river since 1967.

  •  Learn more about historic DO levels & recovery

  •  Learn more about DO and Nutrients


Conditions Today

Today, Delaware Estuary water quality is  much improved. DO levels in the Delaware River Estuary are supportive of resident and migratory fish populations; some degree of propagation (i.e., reproduction and juvenile development) is also being observed.

  •  What's DO like today? View Water Quality Data, including current dissolved oxygen levels in the Delaware River

But, we know that early life stages of estuarine fish species are generally more sensitive to DO levels than are the adults living in the river stretches or just passing through these waters to reach spawning areas. 


Looking Ahead

Can the water quality be improved in this section of the estuary to better support fish propagation, especially that of sensitive species, including the endangered Atlantic sturgeon?

To answer this question, in 2017, the DRBC, with its state and federal co-regulators and others, began a multi-year study that included monitoring, research, technical study, modeling and engineering analyses.
Study Begins: DRBC Resolution Approved September 2017

In September 2017, the DRBC unanimously approved Resolution 2017-4 recognizing the significant water quality improvements in the Delaware River Estuary that have occurred and affirming that continued improvement is an important goal.


The Resolution directed staff to:

  • Perform a study to determine the attainability of an improved aquatic life designated use of fish propagation in a 38-mile stretch of the Delaware River Estuary around Philadelphia, Camden & Wilmington

  • Initiate a formal public rulemaking process on a proposed revised designated use and water quality criteria to protect that use and an implementation strategy


The Resolution provided for scientific and technical studies to be performed for the following purposes:

  • To determine the DO requirements, as well as the spatial and temporal distribution of all life stages of important resident and migratory fish species that utilize the estuary;

  • To develop and calibrate a 3D eutrophication model (linked hydrodynamic and water quality models) of the Delaware Estuary and Bay in close coordination with a panel of nationally recognized experts. The model will relate nutrient loads from point (end-of-pipe) and non-point (runoff) sources to DO targets, prepare scenarios to evaluate the attainability of various DO conditions and aquatic life uses and determine load and waste load allocations necessary to achieve attainable aquatic life uses.

  • To evaluate the costs to achieve various levels of nutrient reductions through enhanced wastewater treatment.

  • To perform technical and socioeconomic evaluations of upgrading designated aquatic life uses to include propagation in the portion of the estuary currently designated for fish maintenance only.


Study Area

A 38-mile stretch of the Delaware River Estuary, from Wilmington, Del. to just above the Tacony-Palmyra Bridge (connecting Phila. and N.J.).

It includes DRBC Water Quality Zones 3, 4, and the upper portion of Zone 5.


Study Partners

The DRBC is leading this groundbreaking effort through a collaborative process informed by:

  • DRBC's Water Quality Advisory Committee, a group representing state and federal co-regulators, NGO's, academic institutions, municipal and industrial dischargers and water purveyors

  • Expert Panel of Scientists and Engineers

  • Representatives of DRBC's "co-regulators" - member state agencies and EPA Regions 2 and 3

  • Representatives of point-source dischargers in the estuary (a total 67 provided data for this study)


Monitoring/Data Collection

To support these studies and the development of the eutrophication model, lots of monitoring was needed.

Ambient (surface water) nutrient monitoring, primary productivity and algal speciation studies were completed.

DRBC staff collect water samples to study light extinction. Photo by DRBC. DRBC staff collect water samples to monitor nutrient levels. Photo by DRBC. DRBC staff monitor nutrient levels in the Darby Creek, a Delaware Estuary tributary. Photo by DRBC. DRBC staff collect a water sample from the Schuylkill River to monitor nutrient levels. Photo by DRBC. DRBC staff collect water samples to monitor primary productivity. Photo by DRBC.
Collecting water samples
to look at light extinction
data.		 Nutrient monitoring at
the Calhoun St. Bridge
(Delaware River). 		Nutrient monitoring at
Darby Creek, a Delaware
River tributary.		 Nutrient monitoring at
the Falls Bridge
(Schuylkill River).		 Collecting water samples
to study primary
productivity.
2017 Study Schedule Updated: DRBC Resolution Approved September 2020


Resolution for the Minutes September 2020

On September 10, 2020, at their 3Q Business Meeting, the Commissioners approved a Resolution for the Minutes that modified the schedule adopted by Resolution 2017-4. The change to the schedule was necessary in light of COVID-19-related mitigation measures that affected monitoring efforts, as well as funding constraints.


Study Progress from 2017-2020

  • Input obtained from an Expert Panel on modeling the water quality impacts of nutrient loadings;

  • Research on the dissolved oxygen requirements of key sensitive species completed;

  • Ambient nutrient monitoring and primary productivity and algal speciation studies conducted to support model calibration;

  • Development of a hydrodynamic and eutrophication model;

  • Identification and evaluation of the capital and operating costs required for twelve wastewater treatment plants to implement technologies for achieving higher levels of dissolved oxygen; and

  • Evaluation of the physical, chemical, biological, social and economic factors affecting attainment of uses.
DRAFT Analysis of Attainability: DRBC Publishes Draft Reports September 2022


DRAFT Analysis of Attainability (AA) & Supporting Documents


The draft AA:

  • Describes the results of studies performed with a state-of-the-art hydrodynamic and water quality model, showing the DO improvements to be achieved when ammonia effluent limits are reduced, and identifies the highest attainable dissolved oxygen condition, or HADO.

  • Determines that DO levels are most impacted by summer ammonia loads from nine point sources (Philadelphia Water Department's Southwest, Southeast and Northeast wastewater treatment plants and the plants operated by Camden County Municipal Utilities Authority, City of Wilmington, Gloucester County Utilities Authority, Hamilton Township, DELCORA and Lower Bucks County Joint Municipal Authority).

  • Summarizes the results of cost and affordability evaluations for reducing ammonia discharges to the Delaware River Estuary.

  • Recommends steps for achieving the HADO.

  • Recommends that the Commission initiate a rulemaking process, as outlined in Resolution No. 2017-4, to revise the designated aquatic life uses and develop water quality criteria to support those uses.
NGOs Petition EPA & EPA Determination: December 2022

In April 2022, a group of NGOs sent a petition to the EPA seeking to bypass ongoing DRBC processes and compel EPA to commence a separate action to revise water quality standards for the protection of aquatic life in the Delaware River Estuary. 


NGO Petition & EPA Response: April-May 2022


DRBC Letter to EPA: October 2022


EPA Determination: December 2022

On December 1, 2022, EPA issued a determination that revising the water quality standards for a portion of the Delaware River Estuary is necessary to satisfy the requirements of the Clean Water Act. In doing so, EPA recognized the value of foundational science performed by the DRBC, including to demonstrate that propagation throughout the Estuary is attainable, and the commitment and ongoing work by DRBC and the Estuary states to update the standards.  


DRBC Statement: December 2022

  • On December 1, 2022, the DRBC issued the following statement:

The Delaware River Basin Commission (DRBC) has received a copy of EPA's determination in response to a Petition filed by a group of non-governmental organizations. Staff is reviewing the EPA response with the Commission members and counsel.   

The Petition sought to bypass ongoing DRBC processes and compel EPA to commence a separate action to revise water quality standards for the protection of aquatic life in a portion of the Delaware River Estuary. Because of the significant progress DRBC has already made – working in close collaboration with EPA and state co-regulators – to update the Estuary aquatic life use standards, the Commission viewed the Petition as unnecessary. (See DRBC letter to EPA, October 2022; pdf) Nevertheless, DRBC respects the Administrator's determination and welcomes EPA's continued engagement with DRBC in this effort.  

EPA's response commends DRBC and its member state agencies for the significant water quality improvements realized in the Estuary.  EPA also recognizes the value of foundational science performed by DRBC, including to demonstrate that propagation throughout the Estuary is attainable, and the commitment by DRBC and the Estuary states to update the standards. EPA acknowledges that the timeline for establishing new standards will be accelerated by the "readily available information that DRBC and other stakeholders have generated." The EPA also makes clear it, "acknowledges and appreciates DRBC's and your states' commitment to updating the WQS for the specified zones of the Delaware River Estuary."

Priority actions by the DRBC to revise the Estuary water quality standards to meet Clean Water Act goals are well underway. By resolutions adopted unanimously by the Commission's member states and the United States, the Commission has committed substantial resources over several years to establish the scientific foundation and conduct rulemaking for new standards through a transparent and collaborative process. The body of scientific work that DRBC has delivered supports the inclusion of fish propagation (by multiple species, including the endangered Atlantic Sturgeon) as a designated aquatic life use throughout the Estuary. DRBC-led science also has established the foundation for the development of new dissolved oxygen criteria to support this use. A summary of DRBC's plan for revising the Estuary water quality standards, along with key technical support documents and procedural records, are available on this webpage. 

While EPA's decision has the potential to create a duplicative regulatory process, the DRBC is committed to continuing to work jointly with EPA and state co-regulator agencies in Delaware, New Jersey and Pennsylvania to develop water quality standards using sound science to meet the goals of the Clean Water Act and the Delaware River Basin Comprehensive Plan. The DRBC is equally committed to doing so through a transparent process that engages all concerned stakeholders. The Commission has a successful 61-year history of working collaboratively and delivering regulatory policy to protect and significantly improve water quality in the interstate waters of the Delaware River Estuary and is committed to continuing this critical work.   
DRBC Suspends Rulemaking Action: Resolution Approved September 2023


September 2023 Resolution Suspends DRBC Rulemaking

On September 7, 2023, the Commissioners approved a Resolution for the Minutes to support regulatory efficiency, intergovernmental coordination and clarity to the public in revising the aquatic life designated uses to provide for fish propagation and corresponding water quality criteria for dissolved oxygen in the Delaware River Estuary.

In short, this Resolution for the Minutes suspended, effective immediately, Commission action to develop proposed regulations for public comment upgrading the designated aquatic life use for Water Quality Zones 3 and 4 and the upper portion of Zone 5 to include propagation. It withdrew the DRBC's scheduled commitment to adopt revised DRBC water quality standards for the Delaware River Estuary by March 2025. The USEPA will lead the rulemaking process.  

The DRBC will continue to provide its scientific, technical and engineering assistance to support EPA's process for revising the aquatic life designated uses and corresponding criteria for Water Quality Zones 3 and 4 and the upper portion of Zone 5 of the Delaware River to meet the shared goal of updated water quality standards that improve protections for aquatic life. Staff will continue to coordinate and collaborate with state and federal co-regulators and basin stakeholders during EPA's rulemaking process.


DRBC Statement

For over 60 years, the Delaware River Basin Commission (DRBC or Commission) has worked to protect and improve water quality throughout the Delaware River Basin. The DRBC supports the "fishable" goals of the Clean Water Act and has taken numerous priority actions to advance these goals in the Estuary, the tidal reach of the Delaware River. Most recently, the DRBC developed major science, engineering, and socioeconomic studies that lay a foundation for revised aquatic life water quality standards for the Estuary and rulemaking to adopt these standards. The Commission has consistently engaged stakeholders and the public on these issues through an open and transparent process.

The DRBC supports the adoption of revised water quality standards that protect fish propagation throughout the Estuary. By a Resolution for the Minutes dated September 7, 2023, the Commission has deferred its planned rulemaking on new standards, pending completion of a separate, federal rulemaking announced by the U.S. Environmental Protection Agency on December 1, 2022. The decision to defer DRBC rulemaking is being taken to support regulatory efficiency and intergovernmental coordination. DRBC's action will avoid concurrent notice and comment rulemaking processes to revise standards for the same water body. DRBC staff will continue to work closely with EPA and the Estuary state environmental protection agencies in Delaware, New Jersey and Pennsylvania to support vital water quality improvements.

The EPA is expected to propose a rule revising the designated uses and the water quality criteria required to protect those uses, in portions of the Estuary. The DRBC's scientists and engineers will continue to focus on strategies for implementing the new standards to achieve the measurable water quality improvements the standards are designed to support. The Commission's work will include identifying affected dischargers, developing wasteload allocations and effluent limitations, and considering capital improvement schedules and potential variances. The DRBC will conduct its work in close cooperation with the EPA and Estuary state co-regulators. Importantly, the DRBC will continue to engage stakeholders in the development of strategies, plans, analyses, and, if appropriate, regulations for the implementation of the new aquatic life uses and criteria, primarily through the Commission's long-standing Water Quality Advisory Committee.

The Commission will continue to support and provide resources to the EPA and the Estuary states to meet the shared goal of updated water quality standards that improve protections for aquatic life. The agencies will work together and with stakeholders to implement the improvements we collectively envision. A single, EPA-led rulemaking process will allow for focused engagement by Estuary communities, advocates and regulated entities.

Further questions about the EPA rulemaking process to revise the aquatic life water quality standards for the Delaware River Estuary should be directed to the EPA.
EPA Proposed Rule & Public Process: December 2023 - April 2025


EPA Publishes Proposed Rule: December 2023

On December 14, 2023, the EPA published a proposed rule to revise the aquatic life designated use and dissolved oxygen water quality criteria applicable to Zone 3, Zone 4 and the upper portion of Zone 5 of the Delaware River Estuary.

The publication of this proposed rule represented a milestone in the effort to reach a fishable Delaware River, but is one step in an ongoing process to improve dissolved oxygen levels in the Delaware River Estuary.

The DRBC has been a part of the process leading up to this proposal and will continue to be involved, working with the EPA, our state environmental agencies and stakeholders to plan for the implementation of revised aquatic life use standards to improve water quality in the Delaware River Estuary. We encourage all stakeholders to learn about the proposed rule and engage in the public process. 


EPA Public Hearings & Written Comments: February 2024

The EPA held two public hearings on this proposal on February 6 and 7, 2024. Written comments were due February 20, 2024.

At the February 6, 2024, public hearing, DRBC Executive Director Steve Tambini provided oral testimony for the record.

The DRBC submitted technical written comments for the record on Feb. 20.


Delaware Riverkeeper Sues the EPA

On October 2, 2024, the Delaware Riverkeeper Network and Maya K. van Rossum, the Delaware Riverkeeper, sued the EPA in the United States District Court for the Eastern District of Pennsylvania over the timing of EPA's rulemaking. A notice of intent to sue preceded the complaint on Aug. 2, 2024.

The EPA answered DRN's complaint on December 9, 2024.


Proposed Consent Decree Issued for Public Comment

On January 22, 2025, the EPA announced it had reached a tentative settlement of the litigation with DRN and released a proposed consent decree for public review and comment.

Under the terms of the proposed consent decree, the EPA Administrator would be required to sign a final rule promulgating revised water quality standards for the relevant Delaware River miles on or before June 30, 2025.

The EPA accepted public input on this proposed decree until February 20, 2025. Please direct all questions about this matter to the EPA.


EPA Provides Update on its Process

On April 1, 2025, the EPA issued a news release announcing its plans to finalize the proposed water quality standards.

In the news release, DRBC Executive Director Kristen Bowman Kavanagh was quoted: "EPA's rule, when finalized, will support improved conditions for aquatic life in the Delaware River Estuary, and I am proud of the Delaware River Basin Commission's (DRBC) sound scientific work in the process," said Kristen Bowman Kavanagh, P.E., DRBC's Executive Director. "The DRBC will continue to provide resources and expertise to our member states, EPA and stakeholders to implement the rule."
DRBC's A Pathway to Restoration: Final Reports Published September 2024

In September 2024, the DRBC published A Pathway for Continued Restoration: Improving Dissolved Oxygen in the Delaware River Estuary and related modeling reports that support updating designated uses and associated water quality standards in the Delaware River Estuary to better support fish populations.


Download the Reports


Next Steps

DRBC scientists are currently focused on technical strategies for implementing the new standards, when finalized, to achieve the measurable water quality improvements the standards are designed to support. This work is being conducted in close cooperation with the EPA and Estuary state co-regulators.
Archive: DRBC Study Reports
Archive: DRBC Presentations

View a video of the presentation, courtesy of the NJ-AWRA:
Archive: DRBC Resolutions

During public meetings from 2010 through 2023, the Commission adopted the numbered resolutions (subject to public hearing) and resolutions for the Minutes (not requiring public hearing) listed in chronological order below, results of which were used to support various aspects of the Aquatic Life Designated Use Study.

All are pdfs.