>>351082That's Blind Tarn, just below Brown Pike which we camped right on the edge from, about 20m from the cairn. Gave us a lovely view of the Old Man in the morning. We walked up Walna Scar Road in the evening from the west side valley, setting off from Seathwaite (from where you can see Scafell Pike looming to the North). Dunno if that's the valley you mean, or Levers Water perhaps.
My mate tried to fish in Low Water with a tiny little fishing rod. Obviously caught nothing, but it was fun just lounging around there for a break from the climb down, watching hundreds of people slowly making their way towards the peak.
10/10 mountain, will visit again regularly.