Welcome to the Forum, Michelle. Your post took me off on an interesting tangent. (I often seem to swing off on tangents, lately - sorry).
That was an interesting description of the lake! I looked at your swan observations around Lake Anna. The lake almost a circle! I wondered if it was man made and how such a small lake could be so deep.
I learned that it is a kettle lake - formed when a big piece of glacier calved off a retreating glacier. What an interesting landform!