I got the nickname "Waterdog" as a youngster on Norris Lake in East Tennessee. My dad and some uncles went together and bought a houseboat and we spent many weeks and weekends on it in the summers when I was growing up. They called me a "waterdog" cause I was usually the first one into the lake and ALWAYS the last one to get out. I love to swim and be on, in, or around the water. I was on the swim team in High school and while not always the fastest swimmer, I could hold my own and do all the strokes.
I added "TN" to make "TNwaterdog" for my CB handle back in the 70's when I was living in Ohio and wanted to ackowledge my Tennessee roots. I'm living back in TN now, so it's back to just "Waterdog", "TWD", "the dog", or "bad dog".
Hell, I'll answer to just about anything these days.