Water Quality Standards To Protect Aquatic Life in the Delaware River

What it is

This is a final rule from the U.S. Environmental Protection Agency (EPA) that sets new water quality standards for a stretch of the mainstem Delaware River under the Clean Water Act. It establishes both a formal designated use — protection and propagation of resident and migratory aquatic life — and specific dissolved oxygen criteria to support that use in three management zones of the river.

What it changes

Before this rule, the covered stretch of the Delaware River (river miles 108.4 to 70.0, spanning Zone 3, Zone 4, and the upper portion of Zone 5) lacked a federally enforceable aquatic life protection designation with corresponding dissolved oxygen requirements. The rule sets minimum dissolved oxygen concentration standards that must now be met in those zones, with the rule taking effect November 28, 2025. These federal standards become the legally applicable benchmarks for Clean Water Act programs in that reach of the river, including NPDES discharge permits issued by Delaware, New Jersey, and Pennsylvania. That means permit writers in those states must evaluate whether a discharge has the potential to cause dissolved oxygen levels to drop below the new thresholds, and if so, must impose tighter effluent limits. Waters that still fall short of the standards must be listed as impaired under Clean Water Act Section 303(d).

Who is affected

Industrial facilities and municipal wastewater treatment plants that discharge into the covered river zones — particularly those that release ammonia nitrogen, which depletes oxygen — may face stricter permit conditions requiring reduced discharge concentrations or improved treatment. Municipalities operating combined sewer systems in the Philadelphia area and surrounding region are also potentially affected, as sewer overflow events contribute to oxygen depletion in the same zones. Anglers, commercial fishers, and others who depend on the river’s aquatic life — including oxygen-sensitive species such as Atlantic Sturgeon and American Shad — stand to benefit if the standards result in improved water quality.