Excellent info Paul.
Shallow water may not necessarily be oxygen poor but can have enough oxygen content for bass to be in it, down here where I live air temps can be easily in the 100 's, water temps can be in the 90 's, I can 't speak about other climates because my experience is limited to warm water environments. So why is it that you don 't find the fish in warmer water ? it 's the temperature, bass can survive in 90 degree water easily for extended periods of time, no they are not going to "burn" out, there are two factors to take in consideration:
1.- Like Paul mentioned, methabolic rate, the warmer the water the higher the methabolic rate, it means that the fish has to eat more in order to maintain it 's organism running.
2.- Comfort zone, bass prefer water in the 70-75 degree range, not only it 's methanolic rate is tops at that temp it 's also that they feel comfortable at that temp. It 's just like us, where would you rather be, getting fried at 100 degrees or being in your house with the AC on comfortably sitting on the couch at 65-70 degrees ?
Fish go deeper where the cooler water ( which also has a higher oxygen content ) is or in the shade to be comfortable, that 's why you don 't find them where the water is warmer.