i built a 2 acre pons about 2 1/2 years ago,about 3 months after completing pond i added 1 more acre of water to it.i dug out the shallow ends and did not add any fish,i just let the rain fill the pond up.my fish took to the new area and everything was ok.approx. 5 months ago i added another 1 1/2 acres to the pond again,this time i did add fish.i let the water flow over the dam to fill new section and put fish in new section.i then waited approx. 2 months before i removed the dam to make it one big pond.i have had good luck with ths method.