Holly Buchanan, and her dad Angus, 45, died during the incident, near Inchmoan Island, on Sunday, March 13, 2005.
Mr Buchanan had taken Holly and his other daughter, 15-year-old Chloe, for a trip on the loch in his rigid inflatable boat on the Sunday afternoon when tragedy struck.
Chloe was spotted by two nearby anglers, and raised the alarm, after clinging to the inflatable craft.
Detectives today revealed remains of a human foot found on the shoreline at Inchmoan Island belong to Holly.
Police said the Buchanan family, from Hillhead in Glasgow, are aware of the discovery.
A spokeswoman for Strathclyde Police said: "On November 11, 2012, police received a report of human remains being discovered on the shoreline of Inchmoan Island, Loch Lomond.
"Officers attended and an initial examination revealed that it appeared to be the remains of a human foot, later confirmed following forensic examination at Glasgow University.
"Further inquiries established that on March 13, 2005 a 13-year-old girl, Holly Buchanan, had fallen into the Loch while on a boating trip with her father.
"Despite extensive land and underwater searches being carried out at the time, the bodies of Holly and her father, Angus, were never recovered.
"Further forensic examinations of the remains and other items provided by the family of Holly and Angus have since confirmed the remains to be that of Holly."