Nerodia erythrogaster Plain-bellied Watersnake
Some other names for this species:
Plainbelly Watersnake
Snake Road, La Rue-Pine Hills Ecological Area, Union County, IllinoisApril 23, 2008
Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster)
Next to cottonmouths, the snake I saw the most of in my first morning on the legendary Snake Road were these guys.

The first one is a tiny baby. The youngsters are much more attractively patterned than the rather drab adults.

The next three photos are all of the same large individual. It was on the verge of shedding its skin, and the right eye was covered with the typical opaque blue scale of an about-to-shed snake. The left eye was covered with a yellow flap of skin that might have been just part of a shed in progress but might have been a permanent injury. This combination made its face looked a little grotesque. I first noticed it at the side of the road, but after a few photos it headed into the water, where it lifted its head up in what my sister called the Loch Ness pose. In the third photo it is rubbing its head on a branch, trying to help peel off the shedding skin.

In the last few dozen yards of my hike I came across the amorous couple in the second to last photo. Unfortunately my presence spooked off the smaller male, leaving the larger female behind to glare at me.

Congaree Swamp National Park, Richland County, South CarolinaApril 6, 2013
Plain-bellied Watersnake (Nerodia erythrogaster) Plain-bellied Watersnake (Nerodia erythrogaster)
This large water snake was less wary than average, probably because it couldn't see well since it was about to shed its skin.
Printed references: