Because of road closures, Pam Vera Snyder, 31, and her son, Preston, 9, were taking a different way home when their car was caught in a flash flood around 4:30 p.m. and swept about a half-mile down Manatawny creek, WCAU reported.
Snyder was on the phone with emergency officials for about 45 minutes while water filled her car, and then the call dropped, WFMZ reported.
Rescuers found the car in a creek nearly five hours later.
"Officers attempted to gain access to the female in the vehicle but unfortunately met the same dangers of the high rising waters and current, and we were unable to get close enough to see the vehicle," Douglass Township Police Department Chief John Dzurek told WFMZ.
Numerous water rescue crews helped to remove Snyder and her son, who were pronounced dead at the scene, the Reading Eagle reported. Snyder was 7 months pregnant and was planning to get married in September, WCAU reported.
Officials said it will take some effort to remove the car, which remains in the creek at the bottom of a steep embankment, the Eagle reported.
Authorities said Snyder did nothing wrong.
"When I was driving through the waters myself, I could feel my SUV, which sits pretty high, wanting to drift away," Dzurek told the Eagle. "I was able to get off a little dirt lane, look down and I couldn't see anything, got spun around and tore back through before I became part of it."