anthropic,
I haven't bothered with getting a DO test kit yet, mostly because we don't have a dock or a boat, so I'm not sure how I'd sample water from the deep. I've assumed that we're okay on DO for now since we never saw fish kills before and we've taken more biomass out than we've stocked (removed 30 LMB, 129 BG, a 20 lb GC), though I really should start checking it to know for sure especially since we've started feeding pellets.

Eric,
The main water source is a stream coming off the mountain, which runs through deciduous (mostly maple and oak) forest. As far as I'm aware there were never any mines in our immediate watershed, though I know the creek a mile or so away (around the mountain) has water quality issues due to old coal mine runoff. We're not farmers, but from what I've heard, I believe farmers in this area have to add ag lime to fields before planting anything because the soil in the region is acidic, I think due to the area being dominated by deciduous forests and having clay soils.