Lower Merion Township officials say people at Flat Rock Park in Gladwyne spotted the vehicle partially submerged in the Schuylkill River just after 7 a.m. Sunday.
Officials said rescue crews arrived and were able to get the woman out of the sinking vehicle, but she was pronounced dead at the scene.
The minivan was also recovered, and officials said the woman is believed to have been the only person in the vehicle.
Police say the cause and manner of death are still under investigation. The identity of the woman, believed to be in her 40s, is being withheld pending notification of her relatives.