If the pond fills itself with ground water then it will be very difficult to manage. You want to be able to completely drain and dry the pond at will. Otherwise, too much organic matter will accumulate.
Typically, ponds are built with a cut-and-fill technique and the pond sits somewhat on top of the existing grade rather than being dug down into the ground. First, a drainage ditch is excavated and this soil is used to begin building perimeter berms. Then soil is scraped from the pond bottom to complete berm construction. There is a slight slope on the bottom so the deep end is adjacent to the drainage ditch. The slope of the berm is dictated by the type of soil. The top width of the berm is dictated by the type of access required (foot traffic, small carts, large trucks). There are software programs to do cut-and-fill calculations, but once you understand the concept it can be done with any spreadsheet or calculator.
-steve h