It's easy to see how they got the colloquial name "Snake Bird."
Anhingas are a very old species, dating back in the neighborhood of 20 million years. Their feathers don't trap air like those of modern birds, and become waterlogged quickly. Thus the anhinga does all its swimming underwater, occasionally sticking its head up to breathe, or to turn and swallow a fish that it has speared with its needle sharp beak. The beak is so sharp, and the bird's strike so forceful, that it can impale even tiny minnows.
Periodically anhingas must leave the water, as they have lower body temperatures than other birds and, lacking the insulation provided by feathers that remain dry, they become hypothermic if they remain wet for too long. They laboriously clamber up onto the bank or into a low tree or shrub. Facing away from the sun, they spread their wings like the bird in the previous picture. This dries their feathers, and a special network of blood vessels located in their shoulders picks up the sun's heat and warms them back to "operating temperature."
When chilled they move slowly, and may be approached quite closely. One should remain well out of range of the long neck and beak, though, as they strike like lightning and often go for the eyes of their enemies (as do herons).