HI Andrew,
The lake east of College Rd with Toner Ave on the left was the 4th lake known as Sandy Bottom lake.
On your photo I can see a section of a stone wall which is possibly a piece of the old Burnheads Farm or its wall.
The large sandstone rocks would have came from Hebburn Quarry and there was thousands of them around the lakes. Quarry was situated between the bottom gate of Ellison Park which was close to Campbell Park road and Leslie's Sports field that is now Sullivan Walk housing estate.