Since you mentioned underwater lighting, i will assume that this will be a basin based fountain and not a reservoir with gravel surface.. Liner will work just fine as long as the water level in the basin is kept below grade. When you bring the water level above grade you will devote a lot of time and creative construction in hiding the inevitable folds that will occur. Another thing that should be considered is the construction of a footer foundation for the fountain(s) units.
Not to doubt your word, but 25' diameter is a very large basin. This equates to the equivalent surface area of some Swimming Pools. If this IS correct, then any fountain(s) that are placed should be large enough to ensure proper visual scale.