The woman was identified as 72-year-old Catherine Kelly.
Kelly's body was pulled from the water around 11:20 a.m. at the Whitemarsh Boat Club at 801 Washington Street in Whitemarsh on Wednesday.
Police say when they arrived they were directed to a dock and the body was found underneath.
Kelly's body was spotted by rowers out on the river, police said.
While investigators do not yet know how Kelly ended up in the water, they are investigating the possibility that narcolepsy may have played a role.
Montgomery County coroner Walter Hofman said Kelly was under medical treatment for several problems and was taking medication for them.
They are still trying to determine what medication she was on.
The family reported her missing after she did not show up to Mass on Wednesday morning at St. Matthew the Evangelist Church on Fayette Street. She was last seen the night before when she had dinner with her sister.
When the family went to her home, they found her front door unlocked and all her personal belongings, including her driver's license and glasses at home. Her car was also at home.
They confirm the cause of death to be drowning, however they continue to investigate how she ended up in the river. They suspect she was only in the water for about 2-3 hours.
Whitemarsh police are canvassing the area to try and locate any surveillance video that may have captured Kelly on camera.
Anyone with information is being asked to call Whitemarsh police at 610-825-6530.