Dissolved Oxygen and Nutrients
DRBC's Aquatic Life Designated Use Study: The Next Chapter in Delaware Estuary Water Quality Improvements

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. By the late 1980s, over one billion dollars had been spent on improving wastewater treatment facilities throughout the basin, which benefited communities along the river and strengthened fish populations.

Today, the Delaware River Estuary supports resident fish and migratory fish populations.

But, we know that the 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. 

It's time for the next chapter. Can the water quality be improved in this section of the estuary to better support reproduction and juvenile fish populations, as well as the endangered Atlantic sturgeon? 
Resolution Approved September 2017

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

View Resolution 2017-4 (pdf 249 KB)

The resolution also provides for a formal study to determine the appropriate designated use for a 38-mile stretch of the tidal Delaware River and to provide data and information to establish revised water quality criteria to protect that use.

This stretch of river, from Wilmington, Del. to just above the Tacony-Palmyra Bridge (connecting Phila. and N.J.), includes DRBC Water Quality Zones 3, 4, and the upper portion of Zone 5.

View Map of DRBC Water Quality Zones (pdf 1.3 MB)

The September 2017 Resolution provides for scientific and technical studies to be performed for the following purposes:

  • To conduct additional field studies of the occurrence, spatial and temporal distribution of all life stages of important resident and migratory fish species that utilize the estuary;

  • To determine the DO requirements of these fish species and the oxygen-depleting nutrient loadings from point (end-of-pipe) and non-point (runoff) sources that can be discharged into the tidal river while maintaining the DO levels in the water;

  • To conduct an analysis to determine the attainability of DO requirements and water quality standards that would result in an upgrade in the designated aquatic life use in this 38-mile section of the river, including technical, social and economic factors; and

  • To identify and evaluate opportunities for early action to reduce discharges of oxygen-depleting wastes to this stretch of river in the short term.

DRBC is leading this groundbreaking effort through a collaborative process informed by an Expert Panel of scientists and engineers and in close consultation with its Water Quality Advisory Committee, a group representing state and federal co-regulators, NGO's, academic institutions, municipal and industrial dischargers and water purveyors.

Once the study is complete, the resolution directs the initiation of a formal DRBC rulemaking process to revise the designated aquatic life uses consistent with the results of these scientific and technical studies, as well as with the federal Clean Water Act.

The Commission will issue a final rule and an implementation strategy, with the timeframe dependent on the availability of resources to fund the effort.
2020 Resolution - Updates Schedule Set in 2017

In September 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.

View Resolution for the Minutes adopted September 10, 2020 (pdf 40 KB)


It is important to note that while the work is ongoing, lots of progress has been made to date, including:

  • 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.


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