Me too! (And also how I guessed Kielder Water.)
I've ridden the circuit of Kielder a few times, pleasant, but surprisingly hilly, 26 miles or so.
All on paths which are usually well maintained because Northumbrian Water spends plenty of money on its star piece of infrastructure.
Kielder was created to serve the enormous water demands of heavy industry, coming 'on stream' just as heavy industry died out.
The result is water is never short in this part of the world, and other regions look enviously at the huge amount we have in reserve.
I recall someone from Northumbrian Water said if it didn't rain for several years Kielder would still be more than half full, or something like that.