We had a kid home for lunch from school, around 1960, he decided to dive in the Dismal Swamp Canal for a swim before going back to school. He was bitten 7 times and his body found later that afternoon. He was a good friend of my brother. I've swam many times in that same canal, he just hit a breeding cluster or ball of snakes. Snopes will tell you these are solitary animals, and 95% of the time they are, but they do indeed cluster sometimes, whether for breeding or whatever, I've seen the phenomena several times when I was a kid. They will sometimes get near the surface and look like a ball of giant worms. I'd guess 12-20 snakes in the clusters I've seen.