JDD, Welcome to the forum!
Springs and groundwater are great, BUT, you are stuck with whatever level they are......what gives water, also acts as a drain to the water. If you "line" the pond with clay, it will block ground water and become a conventional pond relying on runoff. A lined pond is much easier to control as far as water level goes....groundwater ponds offer no control because whatever you pump in simply drains back out as the water table drops.
