Tm,
Forgive me for saying so, but a long cement canal 20-25' deep with Hydrilla growing to say 2-3' off the bottom for the only cover doesn't sound like all that great of Big Bass habitat(especially for the Delta). Are you sure there are big girls in there? Would you be comfortable with posting where this is? I don't know the Delta wonderfully well and am trying to figure out where this would be.
Or am I not getting the full picture and this is just a small wintering area connected to better water for other seasons? Can this canal be floated and if so have you tried metering it and marking the location of anything good?
Tight lines,
Wade