yeah ive noticed this actually. In some deeper lakes w a pronounced thermocline up high like in 20-30ft of water there is almost no oxygen below the top break line, I will not mark a single fish below that break. In deeper waters like aeroflex for instance the thermocline fluctuates for some reason (I beleive rain runoff/springs) there will be a less concentrated thermocline but will mark an occasional fish below the bottom of that break, which I guess to be trout only and landlocked salmon in that lake. Bigger reservoirs which are spring fed like RV sometimes show several temp breaks, and u will mark fish even at the bottom in over 100ft of water i those places so there has to be some oxygen there even if its not much. I think swartswood did good by adding the bubblers, it keeps fish healthier and holding over, and keeps better water clarity overall. U can also find lotsa fish sitting close to the bubblers helps keep them concentrated
