The Upper or Great Lake was once the mill lake. It is known that there was a dam on the W side of the Priory in the Middle Ages. A license of 1437 refers to "Les Dammes" in this area. In the C18 the 5th Lord Byron built mock forts and a castle on its banks and kept a 20 gun ship and other vessels for mimic naval warfare. (1)
There is no doubt that this was the monastic mill pond. There are references to both pond and mill in Med MSS. (2)
Grid ref centred.
See M8939 for Priory, M8293 for house, M2640 for watermill.

<1> Thoroton Society, 1919, TTS, p 113 (Published document). SNT344.

<2> Walker Miss, Pers Comm (Personal comment). SNT1390.