1 acre = 43,560 square feet...so, you're a little less than a surface acre...also, general "square" measurement for an acre is 208' x 208'...may need to excavate some dirt from the sides to expand to your desired size, consider that what you move may be, emphasis is May Be, suitable for your dam...soil test and find a pond builder as opposed to a dirt mover...surf this site, it is AWESOME and contains mounds of information !...
Good luck,
Torchy
