I agree with TJ on alot of what he said. It looks like a gorgeous area/pond. And if you have fallen in love with it, some stuff can be worked out but might cost you additional money down the road.
My thoughts-
Get a boat and go out and see what the deepest area is that you can find and measure it. DONT rely on anybodys word. I would not buy it if I couldn't get them to let you do that.
The trees on the dam are troublesome. One good note is that the pine trees do not have a deep root system. They uaually are no more than a foot deep ( my dad had a nursery for most of his life). But the maple trees are a different story.
Do a ariel map search and see what the water depth looks like over the years. Is it constantly low? Has it ever dried up at some point? From the pics, I get the feeling the water is lower than normal. Is it from drought? will it come back up to get more depth to the whole pond?
The brush/briars could be mowed off. Not a big deal if it is taken care of soon. You will probably need a farm tractor in taking care of this much property. Get a brush hog with it. I would buy an old mower, beat the heck out of it cutting the stuff off(up to about an 1" dia) and then get a nice mower once you get it under control.
