Salty oceanwater is creeping up the Delaware River, the source for much of the drinking water for Philadelphia and millions of others, brought on by drought conditions and sea level rise, and prompting officials to tap reservoirs to push the unpotable tide back downstream.

Pennsylvania's largest watershed is facing record-low water levels. As a result, environmental officials are urging residents to practice conservation.

The salt front in the river has encroached well above its normal level and is now near Philadelphia International Airport. It should be 19 miles farther south in Wilmington.

Salt water from the ocean is starting to creep into the Delaware River Basin due to intensifying drought and sea level rise, according to officials.

Drought and sea level rise are causing salty ocean water to creep into the Delaware River, threatening a source of drinking water for Philadelphia, New Jersey and New York City.