It's common to see a big, dark colored bird sitting near the water, all spread out, sometimes turning slowly, head up. It may be an Anhinga, could be a Cormorant. They don't have oil glands, their feathers are not water repellent, but they hunt underwater. After several dives they must dry out their feathers, and in winter, warm up.
The Anhinga has a spear pointed beak, the Cormorant has a hooked tip. Around here the Anhinga is also known as the snake bird, or water turkey.