Nickajack tailwaters is water immediately below Nickajack Dam. Headwaters are upstream, tailwaters downstream... in other words, Chickamauga tailwaters are the exact same spot as Nickajack headwaters.
It is very confusing because some people for instance, fishing in downtown Chattanoga say they were fishing on Nickajack Lake. Other people fishing the exact same spot say they were fishing "below Chickamauga" or "Chickamauga tailwaters," and nobody is lying ... all answers are technically correct. What I don't know is "where do tailwaters actually end?"
It's sort of like the names of mountains around here.... Flat Top Mountain, Mowbry Mountai, Dayton Mountain, Signal Mountain, etc. All are technically on "Walden's Ridge." But different areas of the ridge go by different local names. However there is no distinct border or geographic feature which seperates Flat Top Mountain from Mowbry Mountain. The only real identifying feature is which road you drive up to reach that part of the mountain. emoScratch