Wow, nice lake and great conditions. From my experience a lake with lots of little or smaller fish improves with removing fish from it, they get bigger as you remove them basically. Spring fed is great but that wont introduce DO unless the spring comes in from the side of a hill if you know what I mean. Your water source might hyporheic
http://naturemappingfoundation.org/natmap/water/field/hyporheic_zones.html it's hard to say without seeing how close the river is to your lake/pond. Depth is tricky when digging in water, as you dig lake sediment and garbage will fill in the area that you dig in short order so if you want a 12 foot hole youll have to dig and dig much deeper. If you have a way to drain it that is best. I know this from experience from digging in an area of my lake that literally filled in after excavating it in low water conditions - sediments and debris in a semi suspended state will seek the lowest levels...and this also created an environment for weeds to flourish like mad.
I bet if you thinned the herd in that pond theyd start to grow very well and youd get the "meat" that you want.
Cheers and send more pics!
Louie
