Parched farms, wildfires, and browned vistas are highly visible signs of this fall's drought.

Less visible: Water flow in the Delaware River, which dropped to 60% at Trenton, the regional agency that oversees the river's use said Tuesday.

Officials with the Delaware River Basin Commission (DRBC) said they have released billions of gallons of water from upstream reservoirs to keep the river to acceptable levels in Philadelphia, but that protective measures might have to be taken if conditions persist. That could include reducing more reservoir releases, or diverting water from elsewhere.

DRBC officials said during a virtual public hearing on the drought that salt front in the river has encroached well above its normal level near Wilmington. Currently, it is near Philadelphia International Airport. The salt front is a metric that shows salinity in the tidal portion of the river.

Philadelphia pulls drinking water from the river at its Samuel S. Baxter Water Treatment Plant in Torresdale, which is about 20 miles above the airport.