Im strugglnig with the same thing Stolly, although not sure its water. More overuse and too much descent after a period of doing very little.
It was not stopping me running, but for every run I needed 3days off afterwards.
I have not run since last wednesday, done nothing really and now it seems to have got worse and hurts when I even walk down the slightest hill.
Physio tommorrow, I will listen to what he says, pay attention and build back up slowly.