Responding Mahwah Police Officer Devon Gannon removed his gun belt, tied a rope around his waist and rushed into the icy water.
Right behind him was Officer Greg Lehman.
"They got them out one by one, from Gannon to Lehman to the shore in the pitch-black dark," Mahwah Police Chief James Batelli said.
The woman and three girls -- ages 5, 12 and 13 -- were all fine, as were their rescuers, he said.
The driver, a Mahwah man, took his girlfriend, two daughters and her daughter off-road in his custom-lifted pickup around 8 p.m., the chief said.
The truck got stuck as he tried to cross the swiftly rushing river at Black Bridge, and he got out to get help, Batelli said.
Police got several distress calls soon after.
"By the time the officers got there, the water was up to their knees in the truck," the chief said.
Gannon and Lehman eventually handed the woman and children off to Lt. Phillip Rangel, Sgt. Brendan Mullin and Officers Rosario Zito, Chris Monico, Mazen Landis and David Vega, he said.
Mahwah EMS rendered first aid to the children, Batelli said.
"Further medical assistance was not required," he said.
Given the darkness and strength of the current, the truck was left behind until Saturday morning, the chief said.
Police, meanwhile, were trying to determine why the driver took that route.
"The decision to cross the river in the dark is questionable, at best," Batelli said. "But the investigation is still ongoing and no determination has been made on whether there will be any charges filed."
The chief praised the actions of his officers.
"They're still a little pumped right now," he said, "and they should be. They did a great job."
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