South Jersey farms are fertilizing the Delaware River — and downstream cities are drinking it

Published by NJ Clean Stream  |  Agricultural Runoff Series, Article 1 of 3

Every spring, nitrogen and phosphorus from South Jersey’s farm fields begin their invisible journey through the landscape — leaching through sandy soils, running off during rain events, accumulating in waterways, fueling algal blooms, and ultimately reaching the drinking water intakes of communities that draw their water from the Delaware River. Agricultural runoff is the most significant remaining source of nutrient pollution in many of New Jersey’s waterways — and the least regulated.

The Delaware River watershed and South Jersey agriculture

The Delaware River is the primary drinking water source for approximately 15 million people, including large portions of the Philadelphia metropolitan area, communities in southern New Jersey, and water systems in Delaware. New Jersey’s portion of the Delaware watershed includes the agricultural counties of the Coastal Plain — Salem, Cumberland, Gloucester, Burlington, Atlantic, and parts of Cape May county — where some of the most productive farmland in the northeastern United States produces vegetables, fruits, and grain crops.

South Jersey’s agricultural productivity depends on intensive nutrient management — nitrogen and phosphorus fertilizers and animal manures applied to support high crop yields. In South Jersey’s predominantly sandy, well-drained Coastal Plain soils, nitrate leaches readily to the water table and ultimately to surface water through base flow. The shallow water table and high hydraulic conductivity of Coastal Plain soils make the region among the most hydrologically connected in the northeastern United States — what goes into the soil in a South Jersey farm field reaches surface water faster and more completely than in less permeable environments elsewhere.

Nutrient pollution: what it does to water and who it affects

Eutrophication in estuaries and embayments. In the Delaware Bay estuary and in the tidal portions of rivers draining into it — the Cohansey, the Maurice, the Salem — seasonal algal blooms reduce water clarity, deplete dissolved oxygen as algae decompose, and alter the ecological structure of the estuarine community. Submerged aquatic vegetation — the foundation of the bay’s ecological food web — has declined significantly in the Delaware Bay system over decades, driven in part by chronic nutrient overloading.

Hypoxic and anoxic zones. When algal blooms decompose, they consume dissolved oxygen. In stratified estuarine waters, dissolved oxygen in bottom waters can be depleted to levels that cannot support fish and invertebrate life. The Delaware Bay experiences seasonal hypoxia in its deeper reaches, driven in part by nutrient loading from the watershed.

Harmful algal blooms in drinking water sources. Nutrient loading from agricultural runoff directly fuels cyanobacterial growth in lakes, reservoirs, and slow-moving waterways serving as drinking water sources. As water temperatures rise with climate change, the interaction between warming water and elevated nutrient concentrations creates increasingly favorable conditions for toxic algal bloom formation in New Jersey’s water supply reservoirs.

Nitrate in drinking water. Elevated nitrate from farm fields reaching the shallow aquifer and then base-flowing to surface water creates elevated nitrate concentrations in both surface water intakes and private wells throughout the agricultural counties of South Jersey. Municipal water systems must implement treatment to reduce nitrate below the 10 mg/L MCL, adding costs to water service. Private well users face the health risks directly.

The regulatory gap: why agriculture escapes the Clean Water Act

The Clean Water Act’s permit-based system has been transformatively effective at reducing industrial and municipal point source pollution. Agriculture was specifically exempted. Agricultural stormwater runoff — diffuse, overland flow — is classified as “nonpoint source” pollution and excluded from NPDES permitting requirements.

The comparison that illuminates the inequity: A wastewater treatment plant discharging to a New Jersey river is subject to an NPDES permit specifying the maximum allowable nitrogen and phosphorus discharge. If it exceeds permit limits, it faces enforcement, fines, and court orders. A large crop farm in the Delaware watershed — whose total annual nitrogen loading to watershed streams may exceed the annual discharge of a medium-sized treatment plant — has no NPDES permit, no effluent limits, no reporting requirements, no enforcement exposure, and no public accountability for its contributions to downstream water quality impairment. This is not a regulatory accident. It is a policy choice.

What the data shows about Delaware watershed nutrient loads

The Delaware River Basin Commission has developed nutrient criteria and loading targets for the Delaware Estuary based on the ecological conditions needed to support the bay’s living resources. The gap between current nutrient loads and the loads consistent with meeting those criteria is large. Agricultural nonpoint sources are a significant contributor to that gap — disproportionate relative to the regulatory attention they receive. The next increment of nutrient load reduction needed to meet water quality criteria cannot come from point sources alone, which have already been substantially reduced. It must come from agricultural nonpoint sources.

What NJ Clean Stream is advocating for

  • Mandatory nutrient management plans with verification requirements for all farms above a modest size threshold — providing a baseline accountability framework that voluntary programs alone cannot deliver.
  • TMDL-based load reduction targets for nitrogen and phosphorus in major Delaware watershed tributaries, establishing specific load reduction responsibilities for agricultural and nonpoint sources as well as point sources.
  • Enhanced state cost-share funding for conservation practices, tied to nutrient management plan compliance — providing the financial support that makes conservation practices economically viable for farms on thin margins.
  • A “voluntary first but not voluntary only” framework that sets a credible regulatory backstop if voluntary programs fail to achieve adequate progress toward water quality goals.

This is Article 1 of 3. Article 2 examines why agricultural runoff is regulated far more leniently than industrial discharge — and what other states and regions have done to close the gap. Article 3 explores the best management practices that work and how to make farmers genuine partners in clean water.