From the pictures it does not look like your pond is an acre, I would estimate a half acre or less.
Your pond looks to be circular. To get a good idea of the true size or area of your pond and if it is one acre it will have a diameter of 236ft and a radius of 118ft. The circumference around the top rim should be 740-750ft(diaXpi). Use 3 foot strides to walk around the top rim and see what you get for a distance.
It is definitely an acre pond contrary to the look in the pictures. The acre estimate came from:
1) Measuring with a range finder and calculating as an ellipse. Calculates to .88 acres with this method.
2) Measuring from aerial view of my land and known landmarks I could measure from. This gave me .95 acre.
3) Just now checked with the perimeter pacing and got 268 paces. My stride is 34 inches so = 759 ft circumference = 1.05 acre. This was taken at the inner edge were the water will be not the outside of the dike.
All of the measuring is including the tiny pond since that will become part of the larger pond in the end.
