hows the water quality of the lower ponds now? Do they ever get muddy? Your pond is going to assume the role of collecting most of the sediment that currently flows directly to the lower ponds - keep in mind that if you want pretty clear water you'll have to address the sedimentation inflow from the springs/creeks. Removing more trees will increase the sediment if you don't provide some ground cover vegetation. Also be aware of the amount of nutrients in those lower ponds, you'll be taking on the nutrient load as well.

Before installing a dam on the main pond you can address these issues and have a great pond from the get go.

Mat Peirce
1.25 acre southeast Iowa pond
LMB, BG, YP, WE, HSB, RES, BCP