Mine is a pretty small pool. Lol. 
I actually wonder if the turtle meant to get in the water or just kinda fell in. And I wonder if he's been in it before. I really have no idea how he would get himself out.
		
		
	 
He fell in 100% without a doubt. You won't typically find Eastern Box Turtles in water. You generally find them in open fields, pastures, grasslands, and woodlands. I've probably came across 100 or more of them in my lifetime. Only once have I found one in an actual body of water. It was in a small portion of non-flowing, still standing water that had remained left over in a dry creek bed. 
Although it's rare, at times they will find a small, shallow body of water to "soak" in. This is only done out of desperation when needing to cool off very quickly. Think in terms of simply sitting in a puddle momentarily. Just long enough for their body temperature to go back down to a normal level. But more times than not, they won't choose an actual body of water. Unless it's basically their equivalent to a turtle emergency, they will just about always burrow under a damp log, wet dirt, moist pile of leaves, or other similar vegetation instead. Really just anything that has some moisture to it. They are also known to completely submerge in mud for multiple days in a row during extremely hot periods of time. 
They are definitely more suited for drier terrain than water. That much is certain. They would easily drown in a larger body of water, especially if it is moving/flowing.
There are 4 recognized species of Box Turtles. There are about 15-16 different types of subspecies found all through out North America though. Only one (Coahuilan Box Turtle) is found permanently living in and around a body of water. They actually spend 90% of their time in water. They are usually found in marshes, or springs. They are endangered, and are only found in Mexico. It's safe to say that you won't find them anywhere in TN. It doesn't look like your typical Box Turtle were all use to seeing in TN either. They don't have yellow on their shells.
Ohh yeah, and don't ask me how I know so much about turtles for nothing. 
