The Delaware River has made a marked recovery in the half-century since John F. Kennedy’s 1961 Delaware River Basin Commission (DRBC) Compact, Richard Nixon’s 1970 EPA, and the 1970s Federal Clean Water Act Amendments. A first of its kind 1960s Delaware River benefit-cost analysis found it cost-effective to fund a multi-million-dollar waste load abatement program to raise dissolved oxygen levels to boatable and fishable standards to generate economic activity. Scientists have called for raising the 1960s DO standard along the Delaware River from 3.5 mg/l to at least 5 mg/l to protect anadromous American shad and Atlantic sturgeon and address the prospect of rising temperatures, sea levels, and salinity in the estuary. A 21st century marginal abatement cost (MAC) curve analysis shows it to be cost-effective to prioritize agricultural conservation and wastewater treatment investments in the Delaware River watershed to reduce 90% of the pollutant load (30 million lb/yr of nitrogen) for $160 million at 35% of the estimated $449 million annual cost. The estimated annual cost to reduce nitrogen loads and increase dissolved oxygen to meet a more stringent standard in the Delaware River includes $45 million for atmospheric NOX reduction, $130 million for wastewater treatment, $132 million for agriculture conservation, and $141 million for urban stormwater retrofitting.