I'm going to disagree with Sunil slightly on this...and that's a first!
It can be risky business, for virtually no gain, to dig areas of 20 feet depth.
First, unless you know what the composition of the bottom is down to that depth, you are taking a significant risk of compromising your lake's integrity, i.e. ability to hold water. You could hit sand, springs, rock or whatever...its risky. Also, that process will muddy your water significantly, possibly leading to a major fish kill if done in the summer heat. Most important, however, is that you don't need 20 feet depth in Texas, and in fact don't want it for raising bass...do some research on thermoclines.
The only problem I see is that if you have significant areas in less than 3 feet of water, you will have problems with weeds...those can be addressed with grass carp and other controls.
I would not at all consider digging out to 20 feet.
