Geograph - photograph every grid square

Once a reservoir, always a reservoir? This is obviously a man-made water body as it is nowhere to be seen on the first 1850s Ordnance Survey map of this area. It first appears on their 1890s map and has forever since been denoted as a 'reservoir'. Even though now it obviously doesn't function as one (and the OS paper map of this area was surveyed unusually recently, in 2021). But I suppose a road remains a road if it is still able to provide it's original purpose, notwithstanding traffic levels. So perhaps the same reasoning can be applied to reservoirs.
It is accessed by a wooden gate just off the footpath leading to/from Stubb Farm.