I've added on to my pond 6 times in the last several years.I started with a 3 acre pond and now up to 6.25 acres.I did not let any water out of my pond when i added new sections.The way i did it was dig the new section then cut a low spot in levee to the point if it rains the water flows into the new section not the overflow ditch that it would normally go in.After new pond fills with water bring track hoe back and dig out old levee connecting the ponds together.I've had real good luck with this system,only problem i do have,while removing levee the water gets muddy digging the old levee out.