James Derrick
Hi,
The 1955-61 &OS map and my memory suggests Meggie's Burn runs nearby, but I thought this is an older disused Blyth Water Works reservoir? 
Based on memory, and out of copyright OS, I've added old names:
https://maps.nls.uk/geo/explore/#zoom=17&lat=55.09952&lon=-1.51443&layers=168&b=1

Would you call it something else please?

Happy Mapping,

James