As summer progress in lakes and reservoirs find the thermocline and follow it to the shore. Fish from that depth and shallower. Natural lakes, depending on water clarity, can have deep weed beds that keep the depths rich in oxygen. There are weed beds down to 25'. In mid-summer this is where the bass are located.
Reservoirs are somewhat different.
Usually, there was a deep cut in the ground with a creek flowing through it. A dam was built and the area was flooded. Reservoirs fall into three main categories, canyon, mid-depth and shallow. Years ago every effort was made to clean the bottom of new reservoirs of their debris and structure. Nowadays, every effort is made to maintain as much bottom structure as possible.