Eddie,
We are also in the midst of a pond project, and when we purchased our property there was a small (150' dia) dish of water within the proposed site. The realtor and owner told me that it was spring pond...I maintained reservations to the accuracy of their belief, but nonetheless considered it may be correct. I talked with 2 different NRCS offices that I had made acquaintance with during my regional search for the right property, and they both had the same response regarding springs. Basically, a spring passage letting water in can reverse and let it out. The chances increase as the head pressure (created by depth of water) increases. They said that springs near the dam are the largest offender. All that being said, they also indicated that, more times than not, springs don't reverse. If you are experiencing radical changes in water depth based on a spring, it may not be good. The rest of the PB guys with more practical experience can kick in guidance instuctions.
Regarding the squishy soil and some gravel, look out! That doesn't bode well. You definitely want professional oversight.