What could this be?

Ground Under Repair
GUR at Royal Ashdown GC
An unusual water hazard in front of the par 5 fifth hole 'Quabrook' at Royal Ashdown Forest Golf Club is described as Ground Under Repair on their list of local rules.
I will be visiting soon to investigate for myself but in the meantime here is an image from the Geograph website taken by Robin Webster from the Vanguard Way which crosses the golf course.
Vanguard Way - Robin Webster