I once saw a water moccasin swimming up a run in Arlington- at least that’s what everyone who saw it thought it was, and it certainly was pretty big- but unlike Buffalo I wasn’t inclined to grab it for a closer look.
More likely a brown water snake.
Cottonmouth’s most northerly range is southern VA.
As a kid, I used to go to Coles Point VA in the summer and they had a long pontoon bridge over an awesome swamp.
I’d ride my bike over it and the bridge would sink a foot into the murky water and snakes would swim past my feet.
Morons camping there kept slaughtering the harmless brown water snakes, thinking they were Cottons.
That may be where I developed a loathing for snake cruelty.