Keen for a change from my usual rather unproductive Oxon haunts, the draughty hide with no door overlooking a small reedbed came to mind, especially as I'd seen accounts from at least one other Oxon birder, who had had some success there recently.
With the hide being on the western side of the lake, it made sense to me to aim for an afternoon visit, and so after the morning rain had abruptly given way to much sunnier conditions, I set off for the hour long drive via Bicester, arriving around 12:15. I was initially dismayed to find two cars already parked in the tiny area available but relieved when one of the occupants shortly appeared and departed.
I found the hide occupied only by Rob, who it seems spends a great deal of time there. He reported I'd just missed a brief Bittern sighting, but the only previous one had been 3hrs earlier, and that there was now probably only one bird present. He also said that the high current water level was reducing the number of Bittern sightings considerably.
However after a mere hour of waiting, I spotted a familiar shape at the right hand edge of the right hand channel through the reeds. The Bittern then proceeded to wade/swim across the few meters of open water, taking about 20 sec to do so. Only when it had almost disappeared again did it emerge into sunlight (for about 1 second). Prior to that it had been in shade which gave a dark silhouette against the bright water.
For a larger image, go to this page on my website
Thereafter, the sun soon left the whole reed bed area but I spent a further couple of hours there without any repeat Bittern sightings, leaving around 15:15. Thanks to Rob for entertaining me with a succession of his phone-scoped videos, which included a remarkable one of a Water Rail attempting to drown a Kingfisher (that eventually escaped and managed to fly off, albeit weakly).
Talking of Water Rails, one was visible here for long periods and once it came to the near shore and very briefly posed for a photo.