Wow, sounds like your well will never run dry.
It sounds like this underground flow may source water for other folks? If so, I would be very aware of legal problems that may occur if you do something in your pond such as pest control and it makes its way into the water source. Also on private land I would never sign up for something that forced me to allow it to be used by the public, again liability issues as well as privacy.
With that said, if there is an underground creek, your drainage may be really good, meaning building a pond may be very difficult without decent materials and/or large water level fluctuations.
Sounds like you will have no trouble filling it though. Keep us posted.
