Drought causes salt water to creep up the Delaware River, where much of Philadelphia’s drinking water comes from

TRENTON, NJ (AP) — Salty seawater is creeping up the Delaware River, where much of the drinking water comes from for Philadelphia and millions of others. This is due to drought conditions and sea level rise, prompting authorities to tap reservoirs to pressure the drinkable tide back downstream.

Officials say there is no immediate threat to drinking water yet, but they are monitoring the drought’s impact on the river and considering options for the future if more droughts hit the area.

A closer look at the creeping salt front:

What is the Salt Front?

At the salt front or salt line, salt water from the sea and fresh water in the river meet. That limit is usually somewhere near Wilmington, Delaware, but the recent drought in the Northeast has pushed it about 20 miles north, around Philadelphia International Airport.

Why is it important?

The further upstream the pipe runs, the closer it comes to the drinking water intake points that authorities have been trying to avoid for decades.

The Delaware River supplies drinking water to around 14 million people, including most of Philadelphia, but also New Jersey and New York. Still, the line lies south of these inlets and below the level it crossed during record drought conditions in the 1960s.

Desalinating salt water that people cannot safely drink is costly, energy-intensive and can raise new problems, such as where to dispose of the highly concentrated brine from the water. It’s also not a viable option, officials say.

“There are alternative sources, but we don’t want to transport bottled water to people,” said Amy Shallcross, water resources operations manager for the Delaware River Basin Commission. “We get nervous when it starts rising near Philadelphia. Currently it is only 18 miles from the drinking water collection points. And sometimes it can shoot upstream very quickly.”

What are the authorities doing about the encroaching salt?

Officials are controlling the salt line by releasing water from two reservoirs, pushing the front downstream. The commission is monitoring flow in Trenton, the furthest point upriver affected by the flood. The flow officer’s goal is roughly equivalent to the amount of water that flows past two Olympic-sized swimming pools per minute. If the rate falls below this, more water is released.

When was the last time salt water flowed this far upstream?

The salt front last reached roughly its current level in 2016, during another drought, officials said.

Does this phenomenon occur elsewhere in the country?

The Delaware River basin isn’t alone in fending off saltwater intrusion, which is exacerbated by rising sea levels and dredged riverbeds to ease navigation, Shallcross said. A so-called “salt wedge” also occurred on the Mississippi in 2023, which led to an increase in the underwater dikes and the entry of drinking water.

What caused the salt water to move upstream?

A rainy start to fall led to drought in parts of the Northeast, including the Delaware Basin. The reduced rainwater has reduced river flow and allowed the denser saltwater to creep upstream.

Did the recent rain help?

Yes, but it’s not enough. The river needs about an inch of rain a week for a while to move the line back to its normal location, Shallcross said.

How are those responsible planning for the future?

The Basin Commission, a federal agency created by Delaware, New Jersey, New York and Pennsylvania to manage the river’s resources, is studying the effects of climate change on water resources and considering other options, including additional storage, Shallcross said. Water managers are also beginning to consider more serious protective measures. “I would say the East is not water rich, we have enough water and we need to recognize that,” she said.