I can’t see the eyes here. He was almost under my foot when I made a turn on a swamp trail. Quick movement stopped me.
He was not very big, under a meter.
A Cottonmouth has vertical slit eyes. Above the triangular head is there but not distinct. However, there is the dark horizontal line running along the side of the head.
He was fast, stopped, then gone.
I’m thinking a Water Snake. Because they can look so similar best to step back and give him space.