Swimming pool?

Or our citerne or a leech farm or a pond. Who knows what to call it? Tricia has been draining and cleaning it for the last few days and currently it sits in the limpid swimming pool camp  - although the temperature of the water might rather defeat that use.
It needs to be used now however as in three weeks, if last year is anything to go by, it will be a soupy green pond. 
That said with so much rain and water about, it might be possible to drain and refill later in the season. Who needs to builds a swimming pool?!

39.6 (sorry forgot it and have edited it in later)