Observed swimming slowly across open water before coming ashore on north back just upstream from Longhorn Dam. If you look closely at the photo you can tell that this is not a big Nerodia. Water moccasins are very buoyant when they swim and the head shape is not that of a watersnake. In my experience Nerodia, whether the local rhombifera or erythrogaster, swim with only the head/neck visible on the surface. This is the second water moccasin I have encountered while out on a field trip with my Field Biology Class. So neat to have the opportunity to show the students and tell them interesting things about this species and water snakes.